I have a Sig "Fastback"... it's basically the "Nightmare", but finished in all Nitron, with rosewood grips. Long story short - love the gun and it functions very, very well.
The only down-side is that the slide profile is not traditional 1911, so many holsters will not fit the Sigs that have their more squared-off slides. I had to look a long time to find a holster that I liked, that would fit the Sig as it should.
I've found the Sig to have many options that others don't have that are in the same price range. Nice guns for the money!