I have been skeptical about the utility of swim skins, but decided to get one for a major open water swim race, chiefly as a confidence boost (also the water temps were chilly but not quite wetsuit-cold, so I figured a bit more coverage would also be good). I didn't have a chance to practice with it before the race, so I dove into the water having no idea whether it was going to work well or be terrible. Happily, I can report that it felt AWESOME and gave the sensation of gliding through the water. It was comfortable throughout the 3.5 mile race--not too warm, not restrictive. The bright blue back panel made it easy for my friends to pick me out in the pack. I did think ahead to put on some Glide around the neck/throat and around the shoulder openings--which was a good thing because I noticed some minor chafing after I got home. I am 5'10", 155 lbs (30w and 40c) and the M fit perfectly, though I'm likely at the top range for M to feel comfortable.