I have a 223 round keychain on a retractable lanyard that I clip to my top pocket that works well. I also have a magnetic button that works great, just don't get caught leaving it attached or stuck to the magazine I believe that is still a no no.
I live in California and have a compliant 10 round bullet button OR that came with a muzzle break. I just looked at the S&W site and sure enough, it looks like the are 2 different sku's for the compliant models. If you look under the compliant tab, the CA model is sku# 151009 and the CR, MA, MD...
I picked up an MP15OR on Sunday and had to blow out of work early to hit the range. Got a few add ons, grip, rails, scope, etc. Took 20 rounds to dial in the scope, but it I got it. Love this rifle, just need more ammo!!