I've had two of these over the past ten years. I had shot a G17 before and figured that a full size Glock would make a good vehicle gun. I wouldn't have to worry about the finish getting to beat up, because Glocks are relatively cheap and have super reliability. I just wanted something with a little more power than a 9mm, though. After reading up on some ballistics charts, and reading about the .357 Sig round, the G31 was the one that I wanted! After I got it, I was shocked by how accurate this round is, and due to the shape of the bullet, absolutely no FTF's! I've only had one instance where there was FTE's, but that was due to a couple of bad reloads that were given to me. Never had any problems with factory loads.
The only reason I give it four star rating is that I know not everybody loves the grip on Glocks. Also, the .357 Sig round itself kicks quite a bit more than any 9mm, so don't expect a soft shooting gun. My sister, who's shot it, loves how accurate she is with the round itself, but has a problem with the grip being a little too large for her hands. My hands are pretty good size, so I don't really have a problem with it, as I also own a G21, which is much bigger. But if you can deal with the grip and want outstanding reliability, I recommend you give this one a try.