Yeah, I understand how it works. It's basically a rip-off of the Robart balancer. But it's still a lot more drag than a pin-point touching a magnet. Think about it this way using pretend numbers.

If a balancer held between your fingers has drag of 10 and a magnetic balancer has drag of .001 then the finger balancer has 10,000 times more drag than the magnetic balancer. If the Dubro balancer has only .1 drag then it's still almost zero drag but 100 times more than the magnetic balancer.

On a magnetic balancer, if the propeller is exactly balanced and you lay half an eyelash on a blade near the hub that blade will drop pretty fast. On a 30K rpm motor a propeller that amount out of balance wouldn't be any problem at all.