The listing, 25+ self-adhesive practice stamps has ended.
When learning how to extract self-adhesive stamps from paper, you need practice. I personally know of four methods, and I ruined good stamps practicing them.
Sure, someday these may be definitive collector's items. But more likely, you need to practice your method of removing them from paper (long hot water soak, Ronsonal, Citrus Cleaner…Google will show you tons). Here's a chance to practice for a small investment.
There are also ways of reducing the strong, well soaked stamps you can barely see die to a severe postmark. Again, these make cheap practice fodder.