The Primus is a pendulum based proportional controller that must be leveled manually... Hence the 70 degree limit. I had one and was a good controller once I got the level set correctly. I still use a pendulum based control and they work well when set up correctly.
The problem I had with setting it up manually was it was a best guess where level was. On the Voyager the control actually tells you when it's level... If you follow the instructions.
The P2 or P3 self levels and uses an accelerometer to sense braking speed. Either works much much better than a time based control. As long as you set them up properly
Those who had negative experiences with the pendulum based controls like the Original Primus and the Voyager must not have had the level set correctly because both of mine have been completely smooth and proportional in braking.
The main reason I have not made the jump to a prodigy is because of the boost band aids. The boost button is absent from the voyager and the Primus because you can set the trailer brakes to easily lead the TV brakes by just slightly setting the pendulum more aggressively.
IE when I push my brake pedal before my hydraulics kick in the Voyager has already detected deceleration and a brake signal from my foot touching the breaks and the trailers brakes are already slowing me down. No boost 1,2, or 3 needed
Thanks,
Jeremiah