I have one of the STAR UltraStars and it really is one fantastic pistol. It's a single stack 9mm, 9 + 1 configuration, DA/SA with the safety also working as a decocker. It's a poly frame with metal inserts, and very small, slightly smaller than the SiG 225.
Here's my 225 (top) and my UltraStar.
So why do I think it might be the best 9mm out there?
For one thing, the trigger reset is very short. The grip is large enough to really control the pistol and double or triple taps are a breeze. The slide rides inside the frame instead of over it. Take down is by pushing out a pin and lifting off the slide. Simple and effective. The accuracy is as good, maybe even better than with my 225. Since the slide ride withing the frame, play seems to be almost non existent.
The best thing about them is that you can usually find one for about $200.00, NIB.
Can't rightly say much about upgrades. Not too sure what that would be. Parts are still available and for what normal repair parts for most other pistols cost, you could just buy another one. Or two.
I haven't kept records but I've been beating on it for about three years now. I'd have to guess that it's well over 3K so far. It goes out with me on just about every trip to the range unless I'm really out for fun. Then it's usually an all wheelgun trip.
So far there have been no FTF's or FTE's and it's eaten everything I've feed it from WallyWord White Box to S&B. It does seem to like Gold Dots the best, CorBon next.
Everybody that has shot it has been impressed including SiG, Croation Sensation and SiG shooters. Them shooting 1911s and HiPowers can't shoot it without a couple weeks of deprograming.