Excellent for small/medium chewers
Kongs are as brilliant as you make them - my dog's favourite is to have it stuffed with wet dog food and frozen. In the past we've also tried (small amounts of) cheese or marmite, peanut butter and chicken. They all go down well and if your dog is too quick then try freezing. The only thing I'd say is they're not indestructable. If you have a dog with a big head and/or a particularly strong chewer (and you know if your dog's a strong chewer) then get the black version or they'll chew hunks off it.