I got these to take the chill off my usually cold feet, and they do the trick. I don't use them in the rain, but they have been good in mist / wet roads. As for fit, I got the XLs to cover Fizik VENTO INFINITO KNIT CARBON 2 in 45.5 and they could be a little tighter for my tastes, but definitely no flapping. They go on easily, stay put, and are very orange on my moving feet, recommended.
Got these covers to replace my well-worn Castelli Toe-Thingy covers which were not enough for the weather here in Maine. These are a big improvement in comfort... cold still gets in but a lot less and is now tolerable on 2 to 4 hour rides. These are very tight and probably need to be - I got the size "L" and they just fit with a lot of effort on my size 44 Fizik road shoes. Once they are fitted, it is clear that "L" is the right size, but it is a bit of a struggle at first. Overall, very happy with these covers. The eye-sore yellow color is a big addition to my being visible to distracted drivers too.