Bought so that I could stick an Aquabeat in it for gym sessions after a swim to avoid carrying two MP3 players.
I wouldn't recommend it for swimming. The Aquabeat is much better stuck to your goggles without wires trailing everywhere.
True that the band isn't fully elasticated - the band itself is stretchy neoprene but for some reason they hemmed it with some stiff fabric. I didn't have a problem with keeping it snugly on my arm throughout gym sessions, nor was it uncomfortable. Might just be I'm not as ridiculously hench as the previous reviewer...
Unlike other reviewers, I didn't have any trouble using the Aquabeat while it's inserted. There are only really two big buttons to use that you easily hit through the fabric by poking the top or bottom of the pouch. When it's on, the Aquabeat beeps in the earphones when it's registered a button press and taking the earphone cord out automatically switches the unit off so there isn't really any need to take it out to check if it's on or off.
Only niggle is the shorter of the Aquabeat cords is just a little bit too short for a normal sized chap to wear it on the arm without it tugging slightly on one side of the head, but that isn't the fault of the band.