Thanks for all of the input.
Update: I have used the Leba III for the past week and I am pleased to say that there has been a noticeable difference in Miahs teeth. I can see that the tarter has come off in layers and has gotten lighter in color. I'm not sure what that means but it seems to be working, which is a good thing.
Bad news is that the left over Leba III that the vet gave me is now gone and I am now starting to use the Vetzlife. I am hoping for the same result if not better. Will keep you informed.