works as expected, holds ~20 bbs, and doesn't leak (had mine for about a year). I use it on the WE M&P 40 (or toucan, or big bird) full sized pistol.
green gas (I use propane + oil) can support about 2 full magazines worth of bbs on average
good gas use (no gas hog)
not really anything that would stand out as a con. it works as expected, no negatives so far.