Drs. Foster Smith carries them too:
http://www.drsfostersmith.com/produc...1&N=2002&Nty=1

I think they are fine. Some vet's don't like competition. I know that when I worked at the vet, people wanted to get their animal's RX through Pet Meds and our office manager said we had to make it seem like they got their products in a "questionable manner". That sounds like what your vet is doing.