This is a great magazine. It is very high quality, and it holds a good amount of bbs. Most of the construction if metal, with a few small plastic parts. They are, however, quite expensive. They have a small amount of wobble, but it's nothing major. Be careful not to drop them; I damaged one of them, so now it won't feed, but as long as you're not as careless as I was you should be fine. Overall, these are great magazines, and a must have if you plan on using full auto or three round burst with your m93r.
Holds a lot of gas
Other than these there aren't really any cons to this magazine