Rating: - Pretty damn good. Buy it!
As a former pool lifeguard there's no way I would let anyone in the pool with something like that dangling round their neck. The cord is big enough to go round the waist though, which is a little safer. If your local pool would let you wear it then buy it. It really is fully waterproof and you can just about work the MP3 .... if you know where all the buttons are. It's really difficult to see the screen but I just select my album before getting in.
It's better to use with an armband than using the cord. In fact it would be better if it was easier to secure the bottom of the pack with an armband but there's no real effective way to do that. A small armband fits in the top OK though. However, these really are small gripes and I would definitely recommend this rather than really crap waterproof MP3s that are out there as, no one really has anything good to say about them, and they cost the earth whereas this is only 4 pound something.
It is important to buy a good set of earphones though. But that's another story.