OK, first off, the good bits:
This is a waterproof MP3 player! How cool is that! Swimming 50 lengths of the pool need never be boring again. It works perfectly well underwater and is perfectly audible above all the noise of the splashing.
That said, there are a number of problems with this product that make it a lot less good than it could be.
First, the user interface is extremely basic. Apart from the volume control, it has only 2 buttons to control the playback: next track and previous track. Not even a pause button. If you don't mind which track you listen to next or if you only have a small number of tracks, then that's probably not a problem, but if you have hundreds of different tracks stored on the machine and want to play a specific one, then you're in trouble. Actually, I don't mind this too much because I tend to listen to podcasts and typically only have 3 or 4 of them loaded at any one time, but if you prefer listening to music, I imagine you could find this a real pain.
Of course the advantage to this very basic user interface is that it's very easy to use as you don't have to fiddle with lots of different buttons while you're trying to swim, and maybe that's why they made it that way.
The next drawback is that it seems to be built with buggy software. There is a reset button that you can press with a pen to reboot it if it stops working. I don't know how often this happens, as I've not had mine for very long, but just the second time I used it it had stopped working and needed to be rebooted, so I suspect it could be a depressingly frequent occurrence.
Finally, the earpieces are really not at all well designed. They have some sort of contraption which I suppose is designed to keep them in your ear. If you are from the planet Zarg, perhaps this works very well. If you have a normal humanoid ear, then it's less successful. All I know is that I found them slipping out of place quite a lot while swimming and had to keep re-adjusting them. Perhaps there is a knack to getting them to fit that would make it easier than I found it, but sadly there is no diagram in the instruction manual, so it's hard to know what the manufacturers intended. I did email the contact given on their website for technical support to ask if they could send a diagram, but I never got a reply.
And that is perhaps the most serious criticism of all: it appears that there is no technical support available for this product, given that the email address given for technical support on the website doesn't bother to answer emails.