Most have been cost prohibitive. Toying with ideas,a lack of availability of units one can drive their chair on and operate from it has been a challenge. Eliminating transfer for user high on list,secondary would be of course range and dependability followed by ground clearance combined with stability. Nothing is good without a good demonstration,whatcha got?
Most interesting topic,been trying prototypes (a friend and i) my favorite around 50.000 but not chair accessible,his a three wheel with engine mounted on handle bars(obvious use of arms limits users.)