The difference of crystal knob with other material knobs:

      The crystal knob is not only static beautiful but also dynamic beautiful. It looks very shinning and dynamitic since refracted and reflected light ray from the crystal and like the diamond are setting in the furniture. The plating silver on the bottom enhance the effects which is unique compare with other knobs. 

The difference of crystal knob with Acrylic plastic knob:

       Acrylic plastic easy to be soften at some degree temperature, also  easy to be shaped and made different form knobs. Therefore the price is comparative low. But the  brilliance of Acrylic plastic knob is less dynamic than crystal knobs. It looks dark and will be get darker as time.

You need to distinguish the materials which are made of knobs.