If you set the length of the straps right, it won't flop around, you have to set it just right though which means a lot of readjustments, but once you get it set, it's great. You get a good amount of power transfer. I never tried SPDs or clipless, so I don't know if Power Grips are more or less efficient. My guess would be that clipless is more efficient just for the fact that the pros ride them. How many pro cyclist do you see using Power Grips? But for the layman or laymanette, these are good alternatives to toe clips because it is more comfortable and more efficient.