Review (4/5): A really good idea, but ones has a hole.
My foot size is a 9-9.5 in mens. These fit snug, but not so snug that they feel like they are going to cut off circulation. They did a fantastic job at holding in moisture and helping hydrate my feet. I didn't feel comfortable keeping the socks on all night because of how snug they are. They are sticky enough on the outside that I don't have any concerns walking around in non-carpeted areas. One sort of gross side effect is that they pick up hair off the floor like crazy.
My only complaint is that one of the socks came with a hole in the middle of the bottom of the foot. So, one sock is only useful for the heel of my foot. That is the main reason I got these, but it does mean I have to be careful how much hydration material I put in the sock (I don't want it to leak out).
Overall I think they are a great solution, much better than my makeshift solution of baggies over my socks. As long as you get a good pair, without a hole, they are a great solution for hydrating dry feet.