After initially running pre-mix in my 3-rotor Lancair ES, I recently installed the 20B OMP.  I use a see-through container mounted on the firewall which holds approx. 8 hrs. worth of 2-stroke oil.  This required one of Richard Sohn's OMP adapters.  As the 20B OMP utilizes a computer controlled stepper motor to control oil flow, and I don't have a clue as to how to properly control it in my application, I built a block-off plate with an adjustment screw to replace the stepper motor.  There is a plunger under where the stepper motor is located that controls the amount of oil the OMP injects, and it is very sensitive.  But with a bit of trial and error you can get the mixture right on 1 oz./gallon of fuel burn.  It works great and I no longer pre-mix.  

BTW, I stopped pre-mixing when I realized that the oil was not getting evenly mixed in my fuel tanks due to the numerous baffles inside the tanks.  The only passages through the baffles are some small "mouse holes".  I attribute unevenly mixed 2-stroke oil to some excessive wear on one of my rotor housings.  This wasn't a problem initially as I was using auto gas and hauling it in a fuel trailer.  The 2-stroke got mixed well during the drive to the airport.  I had to switch to 100LL when the gov't. began mandating 10% ethanol in all auto fuels.  (the ethanol was incompatible with the adhesives in my wing tanks).  Adding the 2-stroke during re-fueling was inadequate to get a good even mix of 2-stroke/100LL resulting in engine damage.  At least that's my best guess.  

Also, unlike the pre-mix method, the OMP keeps pumping oil even when the throttle is fully closed.  So, if you pre-mix, be careful of running for too long with the throttle closed like if you are high and need to make a steep descent.  I think the OMP is a better system.

Mark S.