Long term, the gas piston kit will save me ton of cleaning time. But I've never minded that task, and enjoy it actually.
Had several minor challenges in the build, but only one weird showstopper. I had two magazine catches from separate bagged lower parts kits that were a 1/4" longer than carbine spec. Borrowed the correct one from an unused rifle. See attached image. Oddities have been tagged and put in the spare parts bin. If I knew what lower they went to...I'd probably have to build one of whatever it is.

SAA SA-15 Lower
Del-Ton 16" Upper
Seekins MCSR V2 FF Rail
YHM-9383 Low Profile Gas Block
Osprey OPS-416 Gas Piston Kit + nonstandard operating rod for longer barrel nut travel
Magpul MOE-K2 Grip
Magpul CTR Buttstock
Magpul MBUS Gen 2 sights
Gladio Compensator AR15-AM
Midwest Industries KeyMod Panel Kit
Bravo Company Gunfighter Charging Handle Mod 4 (Medium)
Enhanced Trigger Guard, manufacturer uncertain, possibly Field Sport
Fortis QD End Plate
Optics. I'd narrowed my choices to the EOTech EXPS2 or Aimpoint PRO. With my less than 20/20 vision, I think I've reluctantly eliminated the EOTech. A new contender is the Mepro Tru-Dot RDS Red Dot by Meprolight. All are in the same price range give or take $50 from what I can find.