I bought that set back in the late 80's because auto makers were starting to put shields into their doors so slim jims became difficult or impossible to use. That set came with an instruction manual that described some of the technique to employ, and also matched the key shapes to certain types of locks. IIRC, in the Amazon pic, the fourth jiggy down from the left would be the post-'65 Ford key.
Although I bought those because myself or one of my employees would occasionally get locked out of a customer's vehicle, the real value was soon realized. My personal car and shop stereo/alarm demo was my '86 Cougar. Of course, it was the first car I tried to pick. After a little practice, I could open the door and start the car in under 15 seconds. Can you imagine showing this to customers? Slam DUNK instant alarm sale! With the endless procession of various vehicles, I got very good at going out in the parking lot and opening a prospective buyer's car right in front of him/her, pointing out that anybody could get a hold of those jigglers.
As Kevin said, there is a certain amount of Zen involved. Most of the time I practiced with my eyes closed so I could become one with the lock. Some people here know what I mean. However, there were some cars that I could not crack, no matter how much Yoda implored The Force to be with me.
So, for the price, I say have at it. I made so much money with mine, that I should dig them out and have them gold-plated.