these amulets are widely used by buddhist followers and devotees as the Jantra, not just for spiritual enlighten and good Fortune, But also as a shield protection from evil. These amulets are not just made to sell but are blessed by the High priest before they are send to be sold. They have all the required mantra and material needed to keep Oneself spiritually protected, and blessed.
Some may also define it as a small temple of the god with his / her mantra which you carry on yourself everywhere you go.