I don't know that shaving a balloon has any real relevance to shaving yourself. Maybe to a barber learning to shave someone else. You really learn by doing and the feel and feedback you get and there is none with a balloon. I would think you would be better of using a better knife on yourself first but really just using a real blade and starting out slow and with simple strokes is the best way to learn.

As far a strops go I wouldn't spend too much on one either but getting a basic quality strop is not the same as getting the cheapest thing out there. If you go too low grade your whole learning experience will be clouded by poor equipment.