I sold for six years. "Paint protection" is ALMOST a joke. If there is an IRON CLAD guarantee to protect against acid rain, etc., then it MIGHT be worth it. As more and more cars (almost ALL cars now) are covered in base coat clear coat there is almost NO NEED for aftermarket "paint protectant". A few coats a year of clear coat safe wax and you are all set. (Do NOT use a natural shamee to dry a car, it removes wax!)
Undercoat is even more complicated. If you read new car warranties completely

you may find that some manufacturers will VOID the factory corrosion warranty if aftermarket products are applied!! Improperly installed the weap holes in doors can be blocked and the doors won't drain. I have a 1997 Chevy Express Van. It has no aftermarket protection. A few months ago I installed new brakes and rear helper springs. The van was on jack stands. While under the van I gave it a real good inspection. NO corrosion on the body or frame. None.
Don't waste your money. Most of us will be "playing" with these cars and many will "live" inside a garage. If you REALLY want to get rid of the money, send it to ME.