Have one and basically love it. Shot it in a couple matches this year. The only major downside, is that without that big floppy spacer that has been mentioned. The magazines can over insert and prevent the bolt from closing. So I either use the spacer or load my first mag on a closed bolt. If were to go prone or something that would put upward pressure on a non sleeved magazine, it would malfunction after every shot.
As for the preban mag thing, if you don't need a folding rifle and like S&W. I'm a huge fan of the new Response. It takes M&P mags which allows me to use it in PCSL 2gun and share mags, but also can be swapped over to accept Glock mags. Basically, since I got the Response I haven't touched the FPC.