double freewheel kits?
 

I am planning on buying a terratrike. I want to add a motor but cannot use a wheel hub motor (3 speed in the hub). I have only found one place that sells a motor like i want. At cyclone-tw.com they have a double freewheel kit. It seems that it would work good. I just don't want to mount a motor way up front by the pedals on this kind of bike.

Does anyone have any better kits? Any other vendors make something like this? Does anyone have one of these and have any feedback for me?