I bought these as a replacement for my original set of earphones. They have been improved upon since the original version. I find them comfortable and effective.
However I am a leisurely swimmer, don't engage in serious lengths and laps so can't comment on this aspect of using them.
One very important learning curve for me with the Waterproof MP3 and earphones is the importance of separating the earphones from the player when not in use. This is my 3rd Speedo MP3 player, and its taken me this long to understand that leaving the earphones attached when not in use, causes all sorts of problems.