I can personally attest that the first few batches of Sigmas had serious quality issues. Back when the Sigmas were just hitting the market, a large organization purchased a batch of multi-hundreds these guns and we found that about half of them had broken firing pins right out of the box. That sure didn't do much for confidence. Over the next few years, we found firing pin springs and parts were either broken or missing. On some guns, parts of the firing pin mechanism were actually found to be missing, although many did continue function.
I also have seen inside of chambers rust and pit after the guns went through a rain storm but not were cleaned and dried later. Also there were recalls on magazines and other minor issues over the course of their service life.
That all said, S&W had excellent customer service and over the course of carrying these weapons, they were replaced at least once and I think possibly twice with upgraded models at no or minimal charge.
Also, guns that at least came from the factory with all of their parts in working order, functioned very reliably at the range.
They were decent shooting guns that fired and jammed about as often as the Glocks, which means rarely and accuracy was comparable to the Glocks.
However, initital quality of the initital run of guns sucked big time, but this was improved in later models. But in the end the Sigma lacks some of the Glocks features, such tenefer finish, which prevents rusting issues and this is where much of the money is saved.
I was shocked to see how just how much S&W copied the basic Glock design. I totally understand Glock getting a little PO'd when they first came out.
In the end, that organization later switched to Glocks, mainly because the Glock was and continues to be, the industry standard and because I believe there were still some quality issues with some of the guns that couldn't be resolved.