"okay, so with most hi capa mags you wind them up for about a minute and you have to do it again after every 150 or so shots. with this, you wind it up for a while longer and you get about 200 rounds. i personally dont like this, but some might. it becomes extremely hard to spin the wheel towards the end, but you do get more bbs per wind up. unfortunately it leaves about 20 bbs left that do not get fired. so unless you hold your gun upside down to shoot them, you have to re-wind it up. and yes this says sg 552, but it worked fine in my Sig sg 550. hope this helps, and it depends o preference of mags on rather you should get this or not. i recomend the 100 round standard/mid-capa mags they make for the sg-550/552. happy airsofting "