> I suspect that they're better at some kinds of codebases than others.

Probably. My works custom dev agent poops the bed on our front-end monorepo unless you're very careful about context, but then being careful about context is sort of the name of the game anyway...

I'm using them, mainly for scaffolding out test boilerplate (but not actual tests, most of its output there is useless) and so on, or component code structure based on how our codebase works. Basically a way more powerful templating tool I guess.