Have had my VFC for a short bit now. I have had some problems with some magazines. I have tried out some of the other lower cost solutions on mags as well. Here is what I have seen so far.....
VFC hi-cap = decent fit, but does have some feed problems (surprising to me, but maybe it needs to be worked in)
ECHO-1 new series hi-cap = mid to poor fit, very loose on the front end, does not easily "click" into place and does not match up exactly with mag catch.
G&P 130 rd mid-cap = great fit, great lock, great feed and keeps up with the AEG ROF.
MAG 100 (or so) mid-cap