I have several PMM comps on 365-length slides. Shoot them on p365, P365XL, and P365 Macro-sized grip modules. I've shot them side by side with the Macro Comp, and the PMM version is noticeably better at reducing muzzle rise, as noted above, due to it being a true barrel-mounted comp and not a slide-based expansion chamber (as the barrel tilts relative to the slide and thus the holes in the slide must be more oversized to prevent bullet impact).
As to reliability - I run the factory recoil spring assemblies and have had no issues whatsoever with the PMMs.
Something else I've noticed is the aftermarket barrel that comes with the PMM has proven to be EXTREMELY accurate to me. I've shot some of my best 25 yard groups with a centerfire pistol with them - several 5/8" (not a typo) 5-shot groups. And this in a tiny gun. I also have Bar-Sto, KKM, Apex, and several other aftermarket barrels fitted to full-sized pistols, and although with some of them I can shoot sub-1", I was blown away by the performance of the PMM - I would not have believed it had I not seen it myself. To clarify, these were rested groups while I was sighting in my RMS-Cs.
With your thought of putting a PMM on your XL - as you've noted, the overall length is going to be longer (by ~0.6") than the Macro Comp. Perhaps think about getting a regular P365, adding the PMM and a Macro grip module, and you're at the same dimensions as the Macro Comp. I also prefer the curved triggers, so have replaced the modules that had straight triggers with curved ones. Personal preference there, but if you happen to feel the same way, buying a P365 initially will give you the curved trigger.