At the end of the day, this does what it is meant to - plays music underwater whilst you swim! Given that most of us have wanted something like this (or underwater speakers in pools) to be invented and mass produced since we learnt to swim, and one would assume the technology isn't all that easy to perfect (I don't know why, but I would assume they'd have done it earlier if not) then you have to be pleased by the fact that you can finally listen to your favourite tunes whilst engaging in the monotony of lap-swimming. So given that I accept it does what I want it to, I'll focus on criticisms or areas of improvement which will no doubt be made in coming years...
Its a pretty basic no-frills gadget. I couple of big bulky buttons for play, stop, back, forward and volume. Thats it. No way of viewing your tracks etc (I know you can't do this whilst actually swimming, but you might want to get it to a certain place before starting etc) and I'm partly convinced it was playing mine in a random order. Putting music on it is super easy though, just drag and drop, no need to use the special software.
Its not terribly inconspicuous. Though I suppose you could opt for a black one which might help, but I did feel a bit silly with a blue box strapped to my head and certainly got some intrigued looks.
The earphones aren't very comfortable at all, which personally I found annoyed me after a while and needed the occasional stop and fiddle to make sure they were in properly and comfortable. The sound does seem a little inconsistent particularly when swimming fast or turning, as I guess its easy for the water to dislodge them. Its also far too easy to knock them with your arm whilst doing front crawl. I had initially thought it would be held in place by a swimming cap but i actually found it easier without, the elastic nature of the cap seemed to pull it out of your ears!
The sound is pretty basic, but definitely sounds much better underwater than in the dry, which is rather clever...unless you're one of those swimmers who doesn't like to get your hair wet!!
But essentially, if you're content with something basic to end the boredom of swimming and you can cope with odd looks and the occasional readjustment, then I'd say this is a good buy! After all, what choice do we have?!