I’ve made the Freesewing Bruce boxer briefs and they fitted very well. (They’re designed to not come all the way up to your waist, and I dislike that style, but I just extended the pattern up at the top and it worked fine.)

I’ve also attempted the Simon shirt both for myself and for bob and that worked much less well; in particular, the armholes were comically large. Joost (the designer of both Bruce and Simon) has said on Discord that Simon doesn’t work properly for all body shapes, but I do wish they’d put a disclaimer on the website too.

As ewt said, Joost is tall (and he designed a lot of the patterns), so the patterns are likely to adapt better to tallness than to fatness, but I can certainly sympathise with not wanting to be disappointed again (I wish I could get back all those hours and hours and hours I spent trying to make Simon work).