I was an original beta tester for the version 1 AFS by GG. Although I know improvements have been made to the new mass market AFS, I still think it is alot of hassle for the utility you get from it. The beta version I tested was difficult to get to work properly, difficult to set up, & very unstable and touchy(forget about putting it in your pocket). It also added extra unstable length to whatever mod it was attached to(I actually, at one point, had it attached to my SB with a 901/510 adapter). The requirement of using specially made atty's was also inconvenient. Don't get me wrong, when it did work properly it was nice and the concept itself was innovative. But, again, in my opinion, the utility gained from it did not outweigh the inherent problems and the price.
I now use a simple spring mod on a regular 510 cart and get just as much utility as I did from the AFS, without any of the hassle.