I've heard of those for cats but not dogs.
The thing about them is, well I don't know about anyone else, but I trim my dog's nails about once every 2 weeks or so. The site says the caps stay on for as long as 3 months. My dog's nails would be so long!!!!! I don't think that's right.
Maybe you can find someone in your area who knows how to dremel dog's nails. This keeps them nice and short and sanded around the edges *S*