I have nylon (plastic) clips and they are really not so great. Mostly they do not hold up to the few rotations it takes me to flip into them (they get torn up from scraping the ground). The ones I have now are really cheap now, and on one side the plastic has chipped/scraped away enough so that the strap is barely held into the clip. This doesn't worry me so much because I figure the strap will hold, but as soon as the strap breaks free I am going to replace them with some metal clips. Or maybe spds, since I already have spd shoes (I got these shimano "sport" shoes with the recessed cleat, I just leave the original plate screwed on and use with the clips/straps--better than my beat-up new balances).