I consider them mainstream as they weren't regional from my understanding, but were nationwide.
They also aren't postcards as they weren't sold as postcards and they weren't designed as postcards. They were sold in vending machines as baseball cards.
There are numerous sets besides just the 1947-66, Stat back and Salutations.
There are some which are tinted.
There are some pricier ones are those from the 1920s.
If you like the old time feel of them, look for some of the boxing, football or hockey ones. There also are movie stars, cowboys and probably a couple others.
If you really are into collecting them, you should seek one of the older vending machines.
Here is some information on them.
http://www.moviecard.com/zamerican/e...itgeneral.html