I have a 940 waterfowl pro and i really like it. I'm looking at the turkey pro, and a pro tactical as well now haha. It's an awesome gun, and I highly value made in USA. As far as semi auto shotguns go, there aren't a lot of others available. But yes, the 940 uses the same optic rail and chokes as the mossberg 500, which I think is a super cool and handy feature.
With certain ammo, my 940 seems to not like to fire all the time. Just winchester waterfowl loads so far. I've been reading a little bit about the 930 having that issue, and guys will swap in extra power 10/22 hammer springs to fix the issue. But, I've ran a decent round count through mine, and I haven't had issues other than the 1 box of waterfowl loads so far.
I've read a number of accounts of guys with berettas and benellis turkey hunting and getting a failure to fire because they didn't drop the bolt hard enough to fully seat. On the 940 the bolt isn't rotating, so I bet that problem is eliminated.
I talked my uncle and my sister in law into buying a 940 on a recent hubting trip as well. If you're thinking about a 940, I recommend the 940.
Buy American, and leave the commie guns alone.