These two get sold as alternatives and they are not. They answer different questions, they fail in different directions, and picking the wrong one first is how teams end up paying for both and using neither.
The short version: a heuristic review tells you what is broken. Usability testing tells you what people believe. If you already know what people believe, buy the review. If you already know what is broken, buy the testing.
What each one actually is
A heuristic review is experienced designers walking your product against a fixed set of principles that are already known to hold, writing down every place it violates one. No users, no recruiting, no scheduling. Two people, the live product, a checklist, a few days. This is what most studios mean by a UX audit, and it is what we run as the free 15-point review.
Usability testing is real people attempting real tasks while somebody watches and stays quiet. You give them a job, not a tour: find a tutor who can teach physics on Tuesday evenings for under a certain rate. Then you watch where they go, what they say out loud, and what they give up on. Recruiting matters more than anything else about it; five people who are not your users will teach you five wrong things confidently.
What a review is good at
Coverage. Five test participants might touch six screens. Two designers can cover the whole product, including the settings, the billing page and the error states that no test session will ever reach on purpose.
Consistency problems. A user hitting four differently behaved buttons on four screens across three weeks will not report it; they will just feel that the product is awkward. Somebody reviewing all four in one afternoon sees it immediately.
Known violations. Empty states with no next step, error messages that do not say which field failed, two controls competing to be the primary action, tap targets too close together. These do not need proving with users. They are already known to cost people, and a review finds them in hours.
Accessibility basics. Keyboard access, visible focus, labelled controls, colour that is not the only signal. A general usability test with sighted mouse users will not surface any of it.
Speed and price. No recruiting means no calendar. This is the whole reason to start here.
What a review is blind to
Vocabulary. Your navigation says Workspaces. Your users say projects, and have never once clicked the thing. No principle catches that, because the label is perfectly well designed; it is simply the wrong word. Only somebody hunting for something in front of you reveals it.
What people think the product is for. Reviewers understand your product before they open it, because they read your brief. That is a permanent handicap. They cannot recover the state of not knowing, and every important first-run problem lives in that state.
What people compare. We designed a tutor search around the fact that choosing a tutor is a comparison task: rate as a two-handle range slider, availability as a day-by-day checklist, and rate and rating pinned in a fixed right-hand column so they line up down the page. Which attributes belong in that fixed column is not a question a checklist answers. It is a question about what parents actually weigh against each other, and you find that out by watching them do it.
The workaround they already have. Users who export to a spreadsheet every Monday because your filter cannot express their real question will not mention it, because to them it is not a problem with your product. It is Monday. You only ever see this in a session.
What testing is blind to
Everything off the path. Testing tells you about the flows you chose to test, and nothing about the rest. A session that goes well is not evidence that the product is fine.
Cumulative wear. Nobody in a forty-minute session experiences the fatigue of using a dense tool for six hours a day, five days a week. For internal tools that is most of the actual experience.
Rare and severe states. Payment declined, session expired mid-form, permission removed while the page is open. These are where products lose people permanently, and they almost never occur naturally in a test.
What participants say about themselves. People are reliable about what they do while you watch and unreliable about what they would do next month. Take behaviour from a session; be careful with predictions.
Where the domain tips the decision
A reviewer’s intuition is calibrated on the products they have used, which are mostly consumer products. The further your users are from that, the less that intuition is worth and the more testing matters.
In a mobile trading app, the product is used with one thumb, usually in a hurry, and every tap moves money. Buy and sell are the only two full-width buttons in the whole product, green and red are reserved strictly for direction, and market depth sits directly beneath the order ticket so the numbers that justify a trade and the button that places it live on one screen. Whether that arrangement matches how a trader actually decides is not something a checklist can confirm. Compliance tools, clinical software and anything the user is licensed to operate sit in the same category.
For a sign-up form or a marketing site, the reverse holds. Those patterns are well understood, and a review will find most of what is wrong for a fraction of the cost.
Five situations, decided
Nothing has shipped. Review, on the prototype. There is nothing to test with users yet that is worth their time.
The product is live and you cannot tell where the problem is. Review first. It is cheaper, it is faster, and its main output is a shorter list of places to look.
You know exactly where people drop off and cannot work out why. Testing, aimed at that flow only. A review will describe the step; it will not tell you what the person was thinking when they closed the tab. A seven-step vehicle registration form we designed is the shape of problem where this applies: a review flags that a long form loses people in the middle, but only a session tells you it is step four, and that it is one specific question people cannot answer without leaving the desk.
Two people on your team disagree about a design. Testing. A review adds a third opinion to an argument that already has two.
You are being asked for evidence by a board or a client. Testing, recorded. Nothing else in this trade travels as well as a clip of a real person failing to complete a task.
The order that wastes least money
Review, fix the obvious, then test what is left.
Testing time is the expensive part, and it should be spent discovering things you could not have known. Spending a session watching somebody struggle with an error message that any reviewer would have flagged in the first hour is a waste of a participant you had to recruit. Clear the known violations first, then put the product in front of people and find out what you were wrong about.
That is why our full audit runs both: a flow-by-flow review, and a usability test with five real users alongside it, so the sessions are spent on the questions the checklist could not settle.
Where to start
If you have not done either, do the cheap one this month. Send a live URL or a test account for the free 15-point review and you get ranked findings back within one working day. Whatever survives that list, unexplained, is your test plan.