I have no clue on facebook. I have no account (nor will I create one).
But on reddit the BFG:XR players, which seem a larger part, seem to like MMS, dunno for sure.
As a developer for Eldar MMS my view will be kinda, yeah, right.
But when someone starts the game I will always tell them to use the official rules first. If they don't like official things only then start delving into fanmade stuff.
If you want a middle ground you can always go:
Corsair Eldar : MSM (this will be largest group of players anyway)
Craftworld Eldar : MMS
Dark Eldar : as is.
Three different vibes.