I have the Jordan Ultima 2000 (no longer made and the company that bought out Jordan has killed the unit).
It is the full porprotional type (Stupid, Pendulem, Linear acceleorometer and porportional from worst to best in my opinion).
The Jordan was only about 140.00 as I remember and didn't tap into the tow vehicle's hydraulic system but had a pull cable that attached to the brake pedal.
It works great, just like the old Kelsey Hayes that hooked into the hydrulic system, only it dosent leak brake fluid on your right foot.
All that being said, having used the stupid, pendulem and full proportional, the proportional is best because it is reading what the tow vehicle's braks are actually doing, not trying to artificially recreate what the tow vehicles brakes are doing.