I’ve been using for a few months. Here is my opinion:

• Translation quality is still far from good, but is good enought to be understandable.
• Can’t translate PDF files (hope it could do it in the future, even if that mean reflowing it)
• The extension allowed to keep translating this tab. That’s a future that, in my opinion, would be highly appreciated in the built-in translator (instead of enabling the "always translate").
• The language choice doesn’t correspond with what I usually need (which is chinese. But I know chinese is notably hard to translate.)
• It seems that translation into french first goes thought a first pass of english translation. While this still produce readable result, targeting english is for now probably the best option (even thought the cost of implementing a new language translation pair doesn’t seems too high, I understand they might prioritise adding more language, at least for now. Actually, I should probably contribute to this myself if I care as much about it)