The Suplex kit must be fitted exactly as in the instructions. It is not difficult, just that the instructions have to be read and understood. I can well believe that an experienced mechanic may think he can do it without reading them but he would be risking getting it wrong. I had to readjust mine after getting it home.
The system does reduce the loads on the stub axle which will lighten the steering, this could be the cause of a slight shimmy because of a reduced damping effect. It would be more noticable on early models that have less castor.