I have tested all of them also.
It is true that BMS Stage 1 does feel like an on/off setting. But, that what lead end user to believe that they get the gain. I had a customer with F13 640i, I installed the JB4 Stage 2 and he came back that he couldn't feel it. After I switch it to a Stage 1, that's when he is happy because he can feel it.
As RC Ultimate, it is much smoother than the BMS Stage 1. My guess it could be because of the hardware and firmware.
While the JB4 Stage 2, it has better control throughout the settings since it have all of the car information from the CAN BUS.
Setting wise, some like it mechanical, some like it via computer. It does confusing why RC started with #8 than #0. But, once you are used to it, it is not that confusing.