Chameleon claims this on their website about clones:

  Why Clones Underperform

  Stable RFID requires accurate timing and tuned antennas for perfect coupling.
  Cloned devices compete on price. Reducing the price means using lower-quality components (less precise, wider tolerance), which results in poor performance. Likewise, lowering testing standards means a cloning factory has fewer rejects - but customers receive devices of unproven stability and performance.