Who built this manual staging RPM controller??

[Eman]

I've never used on but I thought it had to be spring controlled so it had to release when you let go of it. I know some made them and they weren't spring controlled and they would forget to release them and got a thrill in the shutdown area.
Isn't a 2 step controlled by the brake pedal legal in stock? I know many sanctioned bracket races have gone to no box.