I have had a model SW9M for about 10 years. I rarely use it, but started to carry it since I recently got my CCW. I don't know how it compares to other Sigma models, but I am not very pleased with it. Luckily, it was a gift and I did not pay for it!
I was out shooting with my wife and kids last week. My wife wanted to try out my SW9M so I pulled it out and tried to "warm it up" for her by checking it and firing a few rounds through it.
The first problem cropped up when I loaded some military ammo I have and the SW9M wouldn't strike the primer hard enough to fire it. This ammo works fine in my Luger. I switched to commercial ammo and emptied a clip with no more difficulty.
I then handed it to my wife for her turn. On the third round the plastic on the back of the stock broke around the drift pin and the action nearly separated from the grip. Thank goodness I was watching my wife rather than looking down-range at the target. I stopped her immediately and made the gun safe. It was lucky neither of us was hurt.
This particular pistol has been sparingly used, probably no more than 1000 rounds ever fired through it. Over the past year it has been my carry gun because I like feel, the weight and that there's no external mag release or safety to get hung up on the draw. However, I've never cared for the stiff trigger pull and poor accuracy. (Maybe the latter was my fault...LOL!)
You can take what you will from this post, but I know I won't buy another one. I have feverishly researched this exact model since the breakage occurred and have found many first-hand complaints about it. Albeit, the research was done on the internet where anonymity is a shield people use to lie and exaggerate. However, my own experience is enough to make my decision!