I'd be willing to be that the majority of the reliability problems folks have with the Sigma are with the .40 S&W version. The Sigma is pretty light and the slide is fairly light. The .40 S&W is a lot harder on guns than the 9mm is, and the shape of the .40 S&W case (straight walled instead of tapered like the 9mm) and the shape of the bullets generally used for .40 S&W ammunition make it much harder to get to feed 100%. The recoil impulse of the .40 is more abrupt and its more prone to limp wristing malfunctions in lightweight guns.
The Sigma is far from alone in that respect. The huge majority of malfunctioning Glocks I have seen over the years were chambered in .40 S&W, and the same is true of the Beretta 9x series.
I'm not saying that the Sigma 9mm is perfect, or that they don't break, but the huge majority of the problem guns I read about on various threads are .40s.
There are much better guns on the market than the Sigma, but they don't cost less than $300 NIB and many don't have a lifetime warranty.
The Sigma is easily worth what it costs, and its just as good of a pistol as some significantly more expensive ones.
I bought mine as a fun gun, not a defense gun. I don't carry it or use it as a home defense gun, but if its what I had, I wouldn't hesitate to trust if for either role.