I have two 24" 6.5CM builds, one is a Faxon barrel, another is a Criterion. Non-suppressed, both with AGB, rifle gas length. On these two, the single-ejector BCG works just fine. Sewing-machine fine, on all the range trips. 5.3oz buffers, Slash's 308 carbine spring. A variety of factory ammo.
I have another 26" 6.5CM, also with AGB, the much-touted "rifle+2" gas length, tuned correctly for last-round-bolt-hold-open. I was getting occasional failures where the brass didn't get out the port (fast enough?), had a few stovepipes, other weird empty-brass-induced malfunctions (single O-ring under the extractor, normal for mine). Switched out the bolt head (not the carrier), for that Arm-or-Ally Toolcraft dual-ejector, and now it runs like a sewing machine. So, I'm thinking, in some cases that extra oomph is needed, and in other cases it's not needed, would be excess, kick the brass into the next county (regardless, I use a brass catcher).
Like some folks say, "a solution in search of a problem". Well, sometimes you find that problem...
I wouldn't start off a new build with a dual-ejector bolt, but would keep that in my hip pocket if needed. I guess alternately, I could've explored going to a carbine buffer heavier than 5.3oz, but preferred to keep my lowers cook-book standardized for what seems to work across almost all of my 308's and 6.5CM's, and do all the specific tuning in the upper. I do swap them around.