The filters are of course made of plastic, but have a very even effect and produce no noticeable color cast. Priced they are compared to Lee or Tiffen filters naturally ridiculous inexpensive.
In the filter holder of Kamerar compendium two filters lassens superimposed use (stacking), which can enhance the ND filter effect, or combine an ND filter with a graduated filter. I use similar filters in the Cokin system and this also after long use no scratches, etc. You have to get round some care so naturally, whereby the filter bag and the included microfiber cleaning cloth helps.
I would buy it immediately.