I own the 8fields JPC, simply because it was cheap.. and I've been running it for 2 years and I'm honestly impressed it hasn't died yet.
However the TMC JPC is a very close replica to the CRYYE one.
Emerson one I hear is good but maybe not as good as 8Fields for slightly larger price point (don't quote me on that).
In terms of using small mags, you can get pouches on the front of course and leave the kangaroo pouch empty.
Personally I run a triple m4 kydex insert I made, it would be able to hold 6 Arp9 mags easy and tight.