Make your own readers
If you want to cheat at poker or do a magic trick don't use pre-marked cards. They are obvious and have a system to them that can be easily picked up by others.
Readers (marked cards) like these are also a huge chunk of evidence against you if you are discovered to be a cheat at cards.
If you wanna cheat at poker, study Erdnase's Expert At The Card Table, AKA Erdnase.
As for magic, try learning some card forces or a little mentalist psychology.
Pre-marked cards are nothing more than a novelty.