Kwa makes the best gbb products ever.
I have the kwa m9 tactical ptp and I wanted an extra mag.
These mags hold gas very well and on a full fill you can get 1&1/2 's worth of bb's or more off of one fill.
They are very durable too and if you drop it, no worries. They also load really easy.
The only downside is price but since ALL gbb mags are 30+$ I wont put that as a con because it's not like these mags cost more than others.
Solid steel (I think)
high bb capacity
high gas capacity
fair price (not more than others even though it's ptp
easy to load
secure in magwell
as far as gbb mags go, these are the best I have owned.
Rating: [5 of 5 Stars!]