Hi, I'm using G&P midcaps (GP128-P) in my ICS MP5 (MX5-Pro), fit snug and feed perfect.
They are, however, easy to pull down out of the magwell without pushing the mag-release button (but they won't drop out). Probably solvable by grinding a bit of material (steel) of the mag catch-indent on the mag. It has not been an issue for me yet so I've left it as is.