A quick video from Nonocat as gets rockin' and rollin' doing a mag dump of the MP5A5 and MP5K Gas Blowbacks from VFC... "So many have asked/tell me that "the VFC MP5 GBBs aren't that good. Especially feeding and gas efficiency"... In one way or the other.
I personally would reserve this comment for the Stock Gen 1s or the declining QC that may be found in some Gen 2s.