Can I reliably just go ahead and use polonius for my app?

I know it's slow. I'm wondering if it's at least as reliable at preventing UB in safe code as the current borrow checker is. I'd love to turn it on and just go to town with certain patterns that it enables but I definitely don't want any UB.

I don't think it's as reliable in every way yet.

It does compute illegal access errors and illegal subset relations errors, generally described in this chapter of the documentation. The move errors it computes are likely incomplete/buggy. It would also need interacting with the trait solver in order to deal with higher-ranked subtyping.