You had asked which clutch someone felt stood out more than another on another forum. Ill answer it here.
In my opinion EVR are the superior.
Here is why.
Ducabike are no different than any other 'ball on ramp' design. There are 2 traditional ball on ramp designs, one that uses a spider spring to adjust slipper pressure and one that uses coil springs and spacers(the later is easier to tune). STM and EVR are unique to the way they operate. The STM looks fancy but is over complicated for what it does. Uses a ball on ramp hub design (no different than the ducabike)but uses spider springs for all it's clamping n slipper forces including the drive pressure plate. Ducabike and all 'coppies' as well as STM, the ball on ramp are under the bottom pressure plate. When reverse pressures are applied for the slipper function the clutch hub is forced out to release plates. If the hub is worn or notched the slipper feature changes from what you have become used to. EVR is unique to all. It has a secondary hub inside the driven hub that has ramps (on needle bearings) that opperates seperate of the driven hub to push the pressure plates apart. This creates a consistent slipper feel and a longer lasting hub(all the 'ball on ramp designs are steel ball on aluminum ramps and wear into ones other. EVR has a steel secondary slipper hub applying forces to steel needle bearings in the top pressure plate).
Atleast this is my understanding. I know there are different STM clutches but I don't know the difference between them. I use a Kbike slipper clutch(on my dry clutch converted hyper. same as Ducabike). If I had the money I would have an EVR....an EVR with a titanium 48t basket(they are made by Ti mar solutions) But that's just a pipe dream for me.
I'm sure I messed up some names/terms and I'm sure there are spelling/grammar errors. This is how I know these systems to work. I'm sure there there are errors.