Same issue as Marc. I had it set up with a C300 with a 16-35mm and a FS700 with a 24-105. Walking slow was fine, but any quicker walk would cause an unusable about of vibration. I sent it back and had it upgraded with a stronger dual clamping bracket, but the problem still occurred. I suspect its from a slight play in the motor.
On the plus side, It was awesome to use outside in the wind. The rig would get knocked around a bit and the horizon stayed locked.
Luckily Letus is a smaller company so I have been able to talk on the phone with engineers and owner to troubleshoot and refine the product. Their customer service is amazing so I'm planning on working with them to find a solution.