Bests & Worsts Reviews from Amazon

This broke 15 minutes into using it for the first time. I couldn't return it to Amazon so I packaged it up and took it to UPS. $20 to ship it back to the factory. I decided never mind and took it apart at home. As I retired Mechanical Design Engineer with several patents I saw the problem immediately. The percussive threaded shaft is nylon or something similarly soft. This injected molded nylon part cannot take any side loading that happens when you dig the head into your back, side, or leg and then move it around. The nylon eccentric provides the up and down motion produced then the motor rotates. The section that broke is 8mm or 0.315" x about 1/16' thick. It is a good design concept except just poorly implemented. If you buy this be very careful and don't push the handle back and forth while it is against your muscle.