The Sig 1911 Nightmare 5" is bad@$$!! It's like it was made to fit my hand. Hefty, but not heavy. Balanced and tight tolerances. Not to mention the black and silver colors just make the pistol much better looking than your ordinary 1911 models (IMHO).
I've taken it out once and run 100 rounds through it. Functioned 100% as a new Sig ought to, and didn't punish my hand & arm at all.
Picked up a couple of 8rd Wilson Combat Elite Tactical Magazines, and they fit perfectly. Sig made some ergonomic enhancements in the design that supposedly make a big difference compared to the age-old specs. Since this is my first .45 1911, I can't really do a comparison.
The only thing I have heard about this 1911 was the external ejector having problems for a short time, but seems to have been corrected. Should be no issue for new guns, just do some research on used ones to see if they fall in that group.
The slide is slightly wider than a Colt or Remington, so be careful which holsters you choose.