my personal opinion is they are the up and coming thing. i have had the experience of seeing three of these work including my own and i must say i am very impressed.
they seem to have plenty of stamina (comes back after a hard run and there is almost no panting), they all seem to be able to turn on a six pence and have speed to burn but they use it when they need it not like some of the dogs i have owned and seen, flat out from the start only to blow out half way through the run. i suppose what i'm saying is they suit me, the land and quarry that i run. atb adam