Have read a few times that Dr Pulley slider weights have flipped over while in use. Some say that is because they were installed incorrectly - or not held properly during installation. This is mentioned in this video made by the TechPulley folks.
I've not had a problem with Dr P's flipping in a Suzuki, Honda or Kymco scooter.
Stig
PS: this video shows the experience I had when installing Dr Pulley's in my Burgman. Lowered RPM's by 1,000 at highway speed.