I have no issue with using something like a thundercap as an aid to training. My trainer had me using something akin to a thundershirt in conjunction with other techniques to get my dog over her fear of my new car. Aids like that play on a dog's psychology of what they associate with safety and security. You put them on when the dog is calm, and it helps keep them in that state while you work with them in an anxiety inducing situation, in my case, the car. Once they realize that the scary situation isn't so scary after all, usually you can remove it for the rest of the training session. With my dog, I'd put the shirt on her, get her to jump in the car, use the other calming techniques if she started shaking. Then I'd close the door, start the car, usually have to calm her again, then put it in drive. After roughly 10 minutes of driving, she'd settle right down and I could take the shirt off her and she'd stay calm for the rest of the trip. The initial calming times were twice as long when I didn't use the shirt. I used it for a couple of months and now she jumps in quite happily and enjoys the ride.