Published · 10 min read

Watt's steam engine did far more work per ton of coal than the engines it replaced, and Britain went on to burn more coal than ever. William Stanley Jevons explained why in The Coal Question, a book first published in 1865: when each unit of work gets cheaper, many more units of work become worth doing, and the saving per engine is swamped by the number of engines. In chapter VII, "Of the Economy of Fuel", he put it without hedging: "It is wholly a confusion of ideas to suppose that the economical use of fuel is equivalent to a diminished consumption. The very contrary is the truth."
PostHog vs Nudgent puts a product analytics platform beside a page audit. PostHog records what people do inside a product. In its own autocapture documentation it "can automatically capture a variety of events in your app without specific tracking code", then plays sessions back, and it runs feature flags and experiments on top. A conversion audit never watches anyone. It reads a single page from the outside and ranks what on that page is likely to make a visitor hesitate, with the evidence attached to the element each finding concerns.
Conversion friction is the name for what that second job hunts: anything on a page that makes a visitor hesitate, get confused, or leave before completing the action the page exists for.
Autocapture did to event tracking roughly what Watt did to coal. Instrumenting a click used to mean a ticket, a developer and a release. Now a snippet goes in once and clicks, pageviews, pageleaves, dead clicks and heatmaps arrive by default. Jevons would have predicted the response: more events captured, and more funnels built on top of them. The part worth testing is whether the thing you installed it for, an answer to why visitors leave, grew at the same rate.
| Feature | Nudgent | PostHog |
|---|---|---|
| Core capability | Reads one page and ranks what is likely to cause hesitation, for human visitors and for AI agents reading it | Records events, sessions and errors inside an instrumented product, then lets a team query them |
| Unit of analysis | A single page | Users and events over time |
| Setup | A URL, no code on your site | An SDK or snippet; autocapture is on by default once installed, then the team defines funnels, flags and experiments |
| Root-cause diagnosis | Ranked findings tied to a named dimension, each with a confidence level | Data the team interprets, with an assistant that can find and summarise replays |
| Experiments | None | Flags and experiments with Bayesian or frequentist statistics |
| Tells you whether a fix worked | No | Yes |
| Pricing model | Early access, no published price | Usage-based, a free allowance per product that resets monthly, no per-seat pricing |
Two rows decide most of this. PostHog can tell you whether a change worked, which an audit cannot, and the experiments row is one we lose outright. The audit attaches a named reason to a specific element, which PostHog leaves to whoever is reading the data.
If your question is what users did inside the product, in what order, and whether last week's change helped, PostHog answers it and an audit does not. Its feature flags let a team "ship code without shipping the feature" and switch a change off without a redeploy. Its experiments exist to "find out whether it actually worked". Those are the straightforward way to close the loop on a fix, and nothing that reads a page from the outside can stand in for them.
PostHog session replay is also good at the job it claims. Its session replay docs describe replay that "plays it back like a DVR" with a synced DevTools panel, so a silent JavaScript error shows up next to the hesitation it caused. For a broken button, that replay is the diagnosis.
PostHog is open source, publishes its roadmap and salaries, and says 97% of its users pay it nothing and more than 500,000 teams use it (PostHog's own homepage claims). It was one of the most-named tools in the community threads we read, and one founder on r/B2BSaaS described the habit that makes it work: "I watch posthog recordings for every new signup in the first 30 days" (AdSuperb8884, June 2026). That is someone doing the reading by hand, which is the right instinct. For an early team with nothing installed, PostHog is usually the right first instrument.
A visitor who leaves your pricing page after eight seconds produces a pageview and a pageleave. The reason they left lives on the page: what it asked for before it explained anything, or the trust question it left open at the moment of the ask. None of that is behaviour, so none of it is in the recording.
Reading the page is a separate act from recording the visit, and no amount of the second turns into the first.
The obvious belief behind cheap capture is that if you record enough, understanding follows. Jevons points the other way. What autocapture made cheap was the event, so events are what multiplied, along with the funnels and dashboards built on them. The number of questions about why visitors leave that a team can answer has no reason to move with them, because the cost of an event was never what held it back.
Events record where something happened, and that it happened. A pageleave on step two, a dead click on a pricing card that looks tappable, a rage click, a replay of forty seconds of scrolling up and down. Each one is a precise location. The reason the visitor hesitated was never emitted by anything, so there is nothing for autocapture to collect, and doubling the capture gives you a sharper map of where people drop off with the same blank where the root cause should be. The limit is structural: no event type for "did not believe the claim" exists to be switched on. One practitioner on r/marketing put the experience plainly: "I've tried heatmaps, session recordings, exit surveys. Get some data but never the full picture." (gogeta7124, June 2026).
PostHog has not ignored this. Its docs offer to "ask PostHog AI to find and summarize" replays, and that is a real help: it gets someone to the right twenty sessions faster than scrubbing two hundred. A summary of what people did is still a summary of behaviour, though. It can tell you most visitors paused at the plan table; why it stopped them stays an inference, drawn from footage that never contained the reason. We made the same argument against a recording tool in the Microsoft Clarity comparison and in the session recordings piece.
We hold ourselves to the same limit. Our own site does not run PostHog. Its first-party event log accepts exactly ten named events, page_view, cta_click and waitlist_submitted among them, and Google Analytics runs behind a consent banner for visitors who allow it. We chose ten deliberately, and none of it can tell us why someone left the early-access page.
No. Nudgent captures no events and replays no sessions. It runs no flags and no experiments, and it will not tell you whether a change you shipped worked. Swap PostHog for an audit and you lose the ability to verify anything.
Both products now talk about agents, so the line needs drawing precisely. PostHog calls itself "your product's context layer", a store that "ingests and stores your analytics, errors, replays, and business data so you and your agents can query and act on it." Those agents query your product data from the inside. The agent plane in an audit concerns outside AI assistants reading a public page on someone's behalf. The agent-plane optimization piece covers ours, and the methodology page lists what an audit does not measure.
If you run PostHog and are wondering what to fix on a page, keep it. Use its funnels and replays to find where the near misses cluster, then have that page read. If you run nothing yet, install the instrument first, because an audit you cannot check against real traffic is an opinion with a score attached. If you are shipping fixes and need to know whether they worked, that is PostHog's job and it does it well.
Jevons's own case is also weaker than this piece has made it sound. Measured rebound for household energy services is usually partial, and whether efficiency ever raises total use across a whole economy, the strong case Jevons argued, is still disputed. Cheap capture does not make anyone understand their product less; it leaves the question of why visitors leave exactly where it was.
Your event count went up this year. Did the list of reasons you could give for why people leave your pricing page get any longer?
No. Nudgent captures no events, replays no sessions and runs no feature flags or experiments, so it cannot tell you what users did inside your product or whether a change you shipped worked. PostHog does both of those jobs well. An audit reads one page from the outside and ranks what on it is likely to make a visitor hesitate. PostHog stays; an audit is useful once it has shown you where people leave and you still cannot say why.
Product analytics records behaviour over time: who clicked what, in what order, and where they dropped off. A conversion audit inspects the page itself and names what on it is likely causing the hesitation, attached to a specific element and ranked by likely impact. Analytics answers where and how many. The audit offers an explanation of why, which can be wrong, and which you can then test with the analytics you already run.
Yes, and that is the sensible order of work. Use PostHog funnels and replays to find the page and step where near misses cluster. Run the audit on that page to get a ranked list of likely causes with the evidence behind each. Ship the top fix behind a flag or as an experiment in PostHog, and let PostHog tell you whether the step actually moved.
It shows what they did, in detail: the scroll, the pause, the click on something that was not a link, the console error at the same moment. The reason has to be inferred by whoever is watching, and PostHog's assistant can find and summarise replays to make that faster. A summary of what people did is still a description of behaviour, so the explanation remains the viewer's call.