For a while, I was using Calyx, and the default install includes an fdroid that did something like this, but it seemed to find anti-features in pretty much every app. I didn't find it terribly useful. 

i don't install many apps, so if I'm installing something it's because I'm pretty sure I need it. I really only want to know if there's a major problem.

Its a problem, yes. So how do we fix it?  There's the F-droid model where things get flagged up that are "anti-features", but I wonder how many people actually read it?

optimism

If it's none, that's good to know too.  But just telling me to review my apps isn't helpful because not everyone has the ability to do that.