I have not personally shot the PMAG adapters - I watched some on-line reviews, read some more, and decided to try it.
If you want to stick with Glock magazines - it's either a dedicated receiver, or an insert - all will work, but expect to have to do a little tweaking with gas, buffers, magazines, and / or ammo with any of these systems.
For a dedicated lower - CMMG's bolt carrier is not slotted for the stock pistol caliber ejector for 9mm, you delete the ejector from your lower with their BCG and barrel.
I wanted a generic rifle lower to work - so went with the PMAG inserts - they were also quite a bit cheaper at one point than 33 round Glock sticks.
I'll either paint the PMAG body, or swap out a base plate - CMMG sells marked PMAGs, but they are expensive.
Why a 9mm rifle? - for me, simple caliber, mild recoil for young / new shooters, another way to shoot without being tied to an ammo shortage in one caliber, and I've got surplus Glock mags.
