This came free with my Zen Stone, so perhaps I should be more grateful. But...
The set-up consists of an adjustable nylon armband with a little velcro at each end, and a rubber housing for the Stone itself.
The armband is far too large for me and I could only get it to work by wrapping it twice around my arm, even on the smallest adjustable setting. Velcro all along the strap would have helped.
The rubber housing for the Stone is functional with cutouts for the controls, USB socket and input jack. There's no cut-out for the power / battery level light but you can see it through the rubber. Just. If you look hard.
The rubber housing is black and of quite a "sticky" rubber - picks up fluff and grot quite easily.
So - it does what it says, as long as your arms aren't as skinny as mine and that you value function over aesthetics.