I got one to use on Sho - he's a DSH with a lot of undercoat, who also replaces his undercoat quickly. It works great on him, but I can't use it too often and can't brush straight down his back because it will remove too much fur there. It obviously doesn't help with the guard hairs he sheds.
Sort of works on Tomas but he's sleek and Siri has very short fur so it doesn't do anything more than petting would.
Completely useless for Sherman. Maybe he's just the type of DLH that it won't work on.
I've used it on other DSHs that have thicker undercoats and by far that seems to be what it's best for. I've also brushed my neighbors DMHs (they don't brush their kitties) and it works on one but not the other.