In my own experience, I find that Expert Review (ER) =followed by=> Usability Testing (UT) works best when you’re approaching a domain you already understand.
When approaching a new domain (e.g. from web to consumer electronics), I find that doing UT ==> ER works much better. People’s behaviours and expectations are waay different across domains. What UT gives you, even a small one, is a tremendous amount of insight in a short amount of time.
Once your “eyes are opened” to your users, ER will be more insightful because then you’ll have some experience with users to guide you. Otherwise, you’ll might end up “barking up the wrong tree”, solving problems with heuristics that might not be big issues at all.
And solving the big issues first is important when first encroaching onto a new domain. If clients can’t see the value of your work, they will think that you simply “don’t get it” and you’re just not right for this domain.
related article: Doing User Research Faster and Cheaper