Sigma had a bumpy start when it first came out. New design and all it's to be expected (happens to alot of firearms in the beginning). Since those early days the Sigma has turned out well and to the best of my knowledge is a fine firearm, after all the S&W M&P is just a more matured, dressed up Sigma
I think you could do alot worse and if it feels good in the hand, wallet and shoots on target I'd say go for it.
There are so many nice pistols out there for sale, you could literally go insane trying to pick the perfect one... (I like Taurus )