Although I have not handled or shot this gun, I find that Smith and Wesson guns very seldom have problems. The number one thing is with these guns - your technique. Take a class - this is the best advice I can give you.
We have them in-stock at ~$419.95; they have been great sellers for us. The SD is very much an "improved Sigma" and provides a bridge in terms of quality/features/price between the Sigmas and the M&Ps.
M&P's aren't much more expensive. I had a sigma in 40 and sold it to up grade to the M&P and couldn't believe how much better it was. So if you have the cash why settle?
Just purchased a M&P 9 a few weeks ago for $416.00 new at my local shop, one of the best buys ive ever made, absolutley love this gun, gonna be around for a long time.
at the Gander in Castleton, i took the SD40 and the 40VE out of the case, field stripped them both, reassembled them in various configurations using parts from both guns and they all function checked ok in whatever combination i put them in. what i'm saying is that as far as i could tell, they're completely interchangeable.
slides to frames, barrels to slides, etc..
the SD uses Sigma mags too.