Chris Swrote a review of Castelli Aero Race Shoe Covers MR on November 4, 2015
Familiarity: I've put it through the wringer
I managed to snag these for free when CC was offering its strava discount, so it's hard to complain on that score. They were a great value. :D
I wore these at road races and in time trials for just about a whole season and got good use out of them. I have an 8.5 shoe and a medium fit perfectly. I did have a problem with the zipper coming undone in a race and a time trial, but that may just be me being careless in setting the zipper.
As the other review mentioned, these covers are very delicate. The front material is a thin lycra that's intended to smooth out the air flow over the shoe. Any friction, like grazing a moving wheel with the toe, damaged the lycra. Not badly, but enough for there to be a hole the size of a pencil's eraser. I didn't have any problem getting these onto my shoe--just being gentle was enough. You can wear these in warm weather and not be in discomfort (for one chilly road race, I put toe covers on underneath and was fine). The dimpled material in back and underneath is delicate as well. There is an opening for the cleat but not the heel, so the back part of my sole wore a hole on the bottom. On the other hand, the fabric contained the hole and it did not allow it to expand. These clearly are for race use only. If you use them when training or commuting, you may as well take your money and set it on fire.
Why I downrated these is because I can't assess whether they accomplished their sole purpose in appreciably reducing drag in light of the cost. Clearly a lot of thought went into these shoe covers, and they look impressive, but I simply don't know if a plain lycra cover (which can be had at half the cost) is much worse. If they're discounted to something close to a plain shoe cover, I think I would get these again. But not at full retail.