You should not be doing heuristic evaluation(HE) or cognitive walkthrough(CW) instead of usability testing, but in addition to. Jeff Sauro wrote couple of great post about both methods: "6 things you didn't know about Heuristic Evaluations" and "What’s the difference between a Heuristic Evaluation and a Cognitive Walkthrough?".
Basically according to Sauro there are 6 things you generally don't hear about heuristic evaluation:
- You need 3-5 evaluators to get results. Different evaluators find different things. Nielsen's research backs this up (check Nielsen(&Molich) references from early 1990s).
- You should do heuristic evaluation in addition to usability testing.
- "Rolf Molich, one of the co-creators of the method said "Heuristic Evaluations are 99% bad" at UPA 2009 on a panel with Jakob Nielsen and Chauncey Wilson on Heuristic Evaluations. His reaction was in large part because HE is being used instead of user-testing and only loosely based on any heuristics."
- Heuristic evaluation is most effective when evaluators are usability experts and domain experts. (Nielsen, 1992).
- There are several sets of heuristics available, not just Nielsen's heuristics.
- There is controversy on how effective heuristic evaluation is (Gray & Salzman, 1998).
The second article is about comparing heuristic evaluation with cognitive walkthrough. Both are inspection methods. Biggest difference is that while HE is about heuristics, CW is about tasks user performs.
The main point is that both of these inspection methods are great when done properly and when usability testing is not possible for some reason. Limited money is generally not a great reason to use these methods instead of usability testing as doing HE or CW well is not that cheap.
The things both methods have in common are:
- Best evaluators are experts in both usability and domain in question.
- Both uncover a lot of usability problems.
- Neither can replace usability testing, but can offer valuable feedback especially in situation where usability testing is unfeasible.
- Both require the expert to take the user's point of view.
- It's best to have multiple evaluators.
- Inspection methods can generally cover larger portions of the UI than usability testing.
Sauro also recommends combining both, in essence doing cognitive walkthrough while looking at the UI with the lens of chosen heuristics.