A friend of mine has one. I have only shot it a couple times. For the price they are not bad guns but they have very heavy triggers. I have two revolvers and the Sigmas trigger is worse than the double action pull on either one of them.
It is very heavy. If you buy one you will probably want to do a trigger job on it.
If you are looking for a SW try looking at a SW99. They are a SW clone of the Walther P99. Cosmetic changes to the shape of the gun are the only difference between the Walther and the SW pistols from what I can gather. They even use the same magazine.
I know this to be true because I own the Walther and use the SW99 mags in it. They are exactly the same mags just with the SW stamp in them.
From what I have read. The SW model is between 100 and 150 less than the Walther.
If you are set on the Sigma also know that the rail on the gun will not work on any lasers or lights. You have to buy an adapter for the Sigma to use anything on it. Last I saw the adapter was about 20.00 shipped.
Trigger aside the Sigma is not a bad gun.