Caution to those who use Keo Grip cleats, these covers were obviously not designed for them. I have used these before on standard Keo cleats, which fit perfectly, but you'll need to stick with those or put in a good deal of wear & tear before they'll stay snug on the Grips (as I did with my previous pair). Also, good luck putting them on in <50F temps.
Kool Kovers may not have the same issues, since they're made of a more flexible rubber, though which unfortunately makes them more prone to falling off. Perhaps they'd fit the Keo Grips better?
Fit aside, definitely a must-have for any cleat, imo.