Doe it really make any difference?
Well, I'm can't say for sure that it does, but I don't think it hurts. OBi support suggested it once when I was having trouble. I'm not savvy enough to know if full duplex is as helpful say QOS in your router, but enabling it does sound good.

Having moved off GV to Obivoice I'm in the middle of paying more attention to my setup and having to do more power cycling than is typical, so my duplex is being reset more often and I'm more aware of losing full.