Yes, the blood (and saliva) testing for dogs and cats is highly debatable. Some vets put a lot of faith into it, others scoff at it. I have two vets, one in each bin...of course!
You can do Google searching and find information that says the blood testing is inaccurate, but you can also find information that is very helpful. I don't know what to think, but for $500 my doggie just might be happier and that would be worth it.
The skin testing is what is used for people. It seems like torture to do that to a dog though since you couldn't tell them WHY we are scratching up and poking their skin. It is not
a comfortable test.