The problem with getting a third party regulator work efficiently with S400/500 is more to do with the removal of that bloody cap on top of the grub screw that adjusts the power externally. Unless one knows how to tackle the problem there is every chance that the valve block will be damaged. It is possible to leave it alone ( much safer from a legal point of view ) but then the full benefits of the regulator will not be had. The consistency will be there for sure but achieving the required efficiency to increase the shot count will be not be there.

A.G