I am familiar with some fluting from my CETME, but can't find much review online for how well their version works in an AR.

DO they extract crap ammo, with less fuss over "spec" or steel case?

Or are they just more work to clean, trap stuff that hurts cycling, and are offset by a tighter match chamber so it is net zero compared to a 'better' M4 chamber?

My 556 AKs eat stuff that chokes my ARs, and I am hoping to bridge the gap and help my budget ammo addition.

I have 3 POF's in 308 caliber, so it may be apples and oranges with you looking at 5.56. Two have the regular chamber, one has the E2. I like the regular chambers better. They all run great, but the E2 does get dirtier in the barrel extension and on the bolt. The others have not had any problems at all. The E2 has failed to extract one time with MEN 83 head stamped milsurp. the extractor tore through the rim and I had to pop out the empty with a cleaning rod. I have shot it since and have not had any other fails. I do not shoot with a suppressor and I do not run steel cased ammo. The E2 is a 14.5, the other 2 are a 16 and a 12.5. On a side note, ALL 3 are accurate as hell out to at least 400 yds with any and all rounds I have put through them.