The Oster Golden A-5 is a great clipper if you are trying to de matt dogs, have to clip through thick coated breeds like cocker spaniels and such...but if you are just grooming your own dogs at home, and they are yorkies...then the 2 speed is really not the clipper for you. The single speed would be just fine.
The 2 speed will work, but you do not really need the second speed (higher RPM's) .
JMHO as a long time groomer.
Sue & Cricket
