They fit well on my size 42 feet, but haven't experienced the 5-star performance other reviewers have described. They do not wick away sweat to the level I would expect - a cheaper pair bought from a weekend market performed better.
Bought for my partner to wear with his plimsoles in summer. They are great because they can not be seen on the outside like traditional socks/trainer socks however he had to spend a a lot of time adjusting them as they kept falling off his foot at the heel. I would purchase again only because he does not like to go sockless in plimsoles but it is a nuisance to consistently adjust them!