The P.E.T.E. is a handy little tool, designed to strengthen the muscles of the embouchure. There are two exercises that the item is designed for, but no doubt others will be developed.
The item itself is very well manufactured; the silver plate is flawless, and it's very comfortable to use. It's also very easy to overdo the exercises, and Warburton do make this point themselves on their instructional videos. A little definitely goes a long way with this product.
I find this to be a very valuable tool for keeping the muscles of the embouchure strong when I have an enforced absence from the horn, such as on long business trips. However, it's not a substitute for practice, and I prefer not to use it as a supplement to practice either, as it's so easy to overdo. This is user error, however, and not a design flaw.