I was impressed with what I saw of them in an M&P15 armorer class.
I've been through a couple of Colt AR armorer classes (and another non-factory armorer class for the A) but I wanted to go through the S&W class to see what I could see regarding their rifles. I already know a couple of owners who have been very pleased with them, too.
As has been said, they've been buying their uppers and lowers (and other parts & assemblies) from the same big names that make them for other good quality brand rifles. (My notes indicate the upper is a 7075 T6 aluminum forging, BTW.)
We were told they've taken delivery of some new forging equipment which will be used to make their own AR uppers & lowers at some point.
Their barrels are made of 4140 steel by their T/C company (known for making excellent quality, accurate barrels). I don't remember if they actually bought their own MP testing equipment or they're still having the testing done by an outside company.
Despite the common advertising hoopla, this is a relatively small industry and there's a lot of products and services being provided to each other among the big companies.
S&W is still making forged billets used in making other 1911's, too.
Overall, I was impressed with the S&W offerings in the AR field.
They'll have a M4 carbine soon (semi/full auto, no plans for burst config).
We were told that demand, especially from foreign countries, has been heavy and consistent for the M&P15. LE interest has been increasing here, as well. A rapidly growing number of satisfied customers.
There's always room for another good build AR rifle/carbine.
As long as it's made of the same good quality parts as other proven names, or properly made & spec'd parts of similar good quality even if made by a new company, a good selection of model configurations and availability are sufficient to meet customer needs (LE/Gov, private and foreign), and increased availability makes for some pricing stability, who cares?
Maybe once I leave CA I'll pick up another good quality AR, this time a M&P15. Then again, maybe not. They can be expensive to feed ... and I've certainly had ample opportunity to do a lot of shooting with a lot of them as a firearms instructor & armorer for some years ... and I already own a good one (Colt). Then again, maybe I'll build another one if I can get a good deal on the components as an armorer.