Not a whole lot bigger, but beefier, and IMHO more reliable. I've never had a P3AT but have heard very mixed reviews. On the other hand, all I hear are good things about most all of the Bersa line of firearms.
I have one. I like it. It has the Parkerized finish.
I have not shot thousands of rounds through it or anything, but I would not call it a piece of junk. Firing the little .380 round into fluid filled bottles produced a more spectacular result than I would have expected. I have not experienced any of the problems that others reported with the weapon itself.
Draw from a pocket holster is a little slower than I anticipated, that is unless your hand is already on it.
My wife, who weighs 100 pounds and carries a .357 magnum, calls it "the girlie gun." :lol:
I've shot one before. It has a bit of muzzle flip, and doesn't fit my large hands well. Feeds ball reliably, I've heard that if you have problems with hollowpoints, polishing the feed-ramp will solve that problem. If you use it as a pocket gun, you're going to need to keep it clean. Pocket-lint will find it's way into the damndest of places.
I thought about getting one, but decided that it was a little too small for my tastes. It reminded me of a Beretta .25 (Tomcat I think) that my father used to have. I couldn't find a way to comfortably and securely hold it. I ended up going with a Walther PPK/S for days that I want something smaller than my Glock 17.