For what its worth, and I am just a road rider, but clipless is the only way to go. But then I don't MTB much (although I do have one) but only a couple times a year or when I need hill work. (Live at base of mountian on BLM road going up said mt.) I would think it would be like having them on my RB more power ect. But like I said I don't MTB much. Its the down hill part I have a problem with.
Any way clipless is best. And didn't take long to get the hang of them, a day or so if that. But then again they are not on a MTB. Desided that I would put them on the MTB if I ever got over the down hill thing.
Have fun and a great new year everone.

Dea