Basically a copy of the Walther P88 with frame mounted ambi safety, non-adjustable trigger stop. IMO, a very nice affordable pistol. Mine has shot very well. Slightly less accurate than the P88 but the P88 is much tighter in tolerances. A little too tight as mine has choked on a few loades with fat heavy bullets (more curvy ogive) as compared to the Thunder9's eat-them-all-up function. Metal quality doesn't seem to be as tough as the Walther's also (i.e. slightly more/faster wear) but it still keeps shooting.
Underrated, IMO, but that is what all Bersa guns were back in the early/mid 90's (even today). Hopefully, if the mag-ban falls, it'll be re-introduced in full size. In the mean time, there is the FireStorm Mini9 and Bersa Mini Thunder9. Essentially cut down versions of the original Thunder9 (the FS Mini9 having the addition of finger grooves as well as both having the locking mechanism, which the Thunder9 would probably now have too).