I've used IS on my Sansa and Zune 30. The Sansa can't do without it, and it doesn't detract from its appearance. The Zune, on the other hand, doesn't look as good with it on, and is already scratch-resistant on its own, in my opinion. Also, at least on the 30, even the "full" shield left WAY too many areas of the Zune exposed.
For the money, a "Best Skin Ever" shield is just as good if you want to try something like the IS and save a lot. They don't offer the lifetime warranty, but if you don't word your warranty claim VERY carefully to ShieldZone (IS), they won't want to honor their warranty anyway. Ask me how I know
Another problem with the IS is that sometimes, during the manufacturing process, the shields can get these micro-scratches. Not a big deal...unless they happen to be in the screen area and you end up seeing a bunch of refracted-light rainbows. Try explaining that to customer service, and they'll blame it on an "installation error." I'm like: You mean to tell me you claim your shield is scratch-proof, but you're telling me the little plastic squeegee you provided to install it scratched it?!
Anyway, save some money, and try the BestSkinEver.