The easy to use and great at cleaning off that hard to get off stuff. I personally use them on 10 and 12mm glass and love them , be carful near rocks and snails , you dont want to damage the blade , but if you do , stop straight away and inspect the blade . if its damages stop using it , and order a new one ;-) .
Each Flipper includes two blades:
Metal blade: Use only on glass tanks.
Plastic blade: Made for acrylic tanks.