Not since the US changed to first-to-file. A patent can be issued to another party and you can be sued for using your own invention. If an examiner never finds your prior art you're still on the hook to deal with the expensive legal process of defense and invalidation.

Elsewhere prior use is an absolute defence against being sued for patent infringement; I've not seen USA caselaw on this specific issue but I can't see how it could be different.

Prior use in public would count as "prior art" and void a patent too.

I don't think first to file is relevant to prior art ( direct from attorneys for things I've tried to patent this year with medical devices)