Ok. The FAQ doesn't help me on this one.
I see from pics that the blocks for Oly uppers use a toggle bar under the mag well to drop mags. The Colt style (Hy-Teck block) uses waht looks to be a push button. Is it left side activated?
From what I can tell neither type uses the std. AR mag catch. If they're the same (left hand operated) and neither operates the bolt hold open, then the root of the decision is whether you want to dedicate a lower for 9mm with a colt system or to get teh Oly and be able to easily swap uppers (.22lr, .223)
These are things I think are right, anyone with either system let me know your experiences, opinions and where I'm wrong.
I have a dedicated .223 20" A2 and a DPMS .22 on another lower that I'd like to put a 9mm on.
Oly uses standard magcatch/drop if you stick to the converted Sten mags that they sell. Mine uses regular sten mags with paddle release on magblock. Hope this helps.
Something to fill the magwell; ala Hy-Tech block---
Add an upper; ala Colt pattern ---