they work fine with my Creative Labs player. I haven't tried them on one of the tiny thumb-drive-sized players, as I don't own one of those. The headphones also work flawlessly with my Lenovo laptop computer's headphone jack.
They're well-constructed mechanically and have a reasonably large adjustment range, and the folding mechanism works well. I should point out that for many MP3 players and computers you will need a 1/4" to 1/8" adapter. It's not obvious on the page, but Sony actually includes that with the headphones. You gently unscrew the 1/4" plug off the end of its connector, and there's a 1/8" plug inside.