I have 2 PROTANK 2 and 2 Evods in use and consequently a relatively high Verschleis these heads. The quality varies greatly. Sometimes all heads work excellent but I already had packages in which 4 have gesifft evils of 5 evaporators from the outset. For the price you can probably expect any sophisticated quality control, but I would rather pay a little more for it and only get heads that work.