I've gotten Elka other toys with this type of generic "Wal Mart dog stuff" label, such as a rubber horse shoe and rubber fire hydrant, both of which have been reasonably sturdy. The balls themselves were the really smelly, don't really bounce well kind. A real bonus of these dog specific tennis balls, though, and this goes for almost every one we've tried: there's less fuzz. Elka really likes peeling the fuzz off of sport tennis balls, which I'm not a fan of.
Once I gave her the tennis balls, we had already gone for our walk this morning (and hour and a half), and played a bit in the back yard with the sport tennis balls. I still use those for basic fetch, as she doesn't have time to settle down and chew them.
Elka carried the first ball around for a little while, after picking it up and dropping it, and bringing it to me and dropping it in my lap, then getting it when I rolled it across the floor. After ten minutes or so, though, she settled into her regular ball-abusing ways, and sort of made a Pac Man out of the first one. Not quite as good a face as with the Patriotic tennis balls (seen here), but amusing, nonetheless.
The second tennis ball had a shorter life, as is the way of things. Really, at this point, Elka seems to get thorough enjoyment out of a short and brutal destruction of a ball. It doesn't bother her much when I take them away, photograph the evidence, and give them the heave-ho.