Lightweight, stays put in most situations (even upside down), easy to use for both playing and transferring files, water resistant and a very reasonable price.
I think the wire which wraps around the back could be adjustable or slightly smaller. And I look forward to the next generation of this Sony Walkman which will hopefully be smaller.
I definitely recommend this Sony Walkman to anyone who uses the gym or enjoys running. I have been using it now for month and I don't go to the gym or running without.