I use Petbucket's service and so far have not had any issues whatsoever.
It is a real bargain and I don't even have to worry if I have Mia's Heartworm or flea and tic meds.
Auto ship is great. Stopping the service....I don't know about yet so we will see. Unfortunately dogs don't live nearly long enough so I will let you know if any issues.
So far everything is great.