As far as my research has gone, it seemed there were a few probs on occasion with some of the .177 mags on S10s. This does NOT mean they all don't work. I have (had, I'm just selling) a .22 and there were absolutely no probs with the mag at all - every time.

The filling system is perhaps open to more leaks because you remove the buddy each time you fill. This is very easy, but I guess it leaves it open to human error and so you'll hear more stories of leaks from this design than from a fixed push on type (IMO).

(someone will probs correct me now )