I have a Sig P239 in .40. The gun has been accurate and reliable for me. I would say it has some disadvantages, including:
1) It is overly large, compared to my Kahr K40. The Kahr is thinner, smaller, easier to conceal and carry.
2) The bore axis is high, giving extra muzzle flip.
3) It is DA/SA. I'm not a fan of DA/SA -- I prefer a gun which has a consistent trigger pull from shot to shot, i.e., SA, DAO, or striker-fired. This is a religious issue, however. Either you like it or you don't.
4) The controls are laid out differently than most guns. In particular, the slide stop is the rear-most control lever. In most semi-auto guns, the slide stop is farther forward. If you change from gun to gun, this may be something you could fumble under stress.
5) The 239 feels unbalanced and top-heavy in my hands.
The 239 is a good gun. But I carry my Kahrs -- my 239 lives in the safe. YMMV.
M1911