Bear spray worked great last week on a 50# unleashed pitbull. Wife and I were on Billy Creek Trail (Pinetop, AZ) for a short walk with my Heeler mix and TW Coonhound (both of our dogs on a leash). Half mile into the walk, an unleashed pit out of nowhere charges at my TW, snarls and goes for the throat. Pit gets a face full of Counter Assault and immediately stops the attack and the offending dog trots back to the owner (who of course plays victim).
My dog took a bit of overspray on the top left side of her neck. Pain in the arse to get all the spray off, but a small price to pay instead of a huge vet bill or dead dog.
I don't have any experience with spray against some meth'ed out transients (plenty of those in PHX/Tempe), but I wouldn't hesitate to use it again against a large, off-leash aggressive dog ready to tangle (also plenty of those in PHX/Tempe).