With respect to delayed blowback: the H & K (Mauser) and Thompson (Blish) configurations are in-line ramp systems; the CMMG configuration is a rotary ramp system; hydraulic buffers are in-line telescopic systems. There are several other delay configurations that have been implemented for firearms use. All provide delay to the initial recoil pulse. All have their pros and cons.
The recoil energy and recoil pulse are quite different for 9mm and 5.56x45. While there are some recoil spring and buffer configurations that can be used in connection with AR-15 pattern firearms for either caliber upper/lower configuration, a single use recoil spring and buffer configuration will have compromises for either or both calibers.
I was already heavy into Glock mags before the CMMG system was introduced. The financial tipping point between using a magwell adapter plus Glock mags or using MEAN Endomags is generally calculated to be five. So as well as the size and weight downsides to Endomags, they would be a total financial loser for me.
With those considerations in mind, I use a magwell adapter and Glock mags in connection with one type of hydraulic buffer and recoil spring for 9mm shooting using a ramped, direct blowback bolt/carrier group; and swap to a different type of hydraulic buffer and recoil spring for (D.I.) 5.56x45 shooting at the same time I swap uppers.
Best of luck with whatever you decide to pursue.
Disclaimer: I have no affiliation with or financial interest in any vendor or manufacturer; and I am not a competitive shooter or a blogger who receives any form of compensation for endorsements or favorable public or private comments. Use of vendor and/or product brand names, if any, is for informational purposes only; and products or services were purchased from regular commercial sources.
Best of luck.
MHO, YMMV, etc. Be well.