This unit has an iRiver iFP-380T MP3 player at its core then adds in a waterproof case for that as well as a waterproof amp and set of underwater headphones to complete the underwater aural excursion. The headphones come with clips that allow them to attach the strap on your goggles.
Then you get underwater surround sound quality audio for however long the 9-volt and AA battery combo lasts. This set is good for 128MB worth of music and a depth of up to 200 feet, which isn’t bad for $99.
There are several issues that come to mind when I even consider scuba diving with something in/on my ears, and all of them point towards it being a bad idea. However, if you are just swimming around in a pool, or snorkeling in a pond or something like that, it might not be a bad investment as it could keep things fun.