Duragrouch

Above, regarding the Origami Bull riding like a full size bike: Good to know. Not a surprise, from what I am seeing. In terms of ride quality, the large tires should compensate for the smaller wheels. But in terms of steering stability, those large, heavy tires and tubes (and 36 spokes and nipples), add rotating inertia (angular momentum), so gyroscopic inertia closer or equal to a large wheel bike with skinnier tires. Also, by my eye, I think that bike has caster/trail toward the large end of typical bikes, especially 20", my guess is perhaps 70mm? Too much above that and you can get "wheel-flop" issues at low speed, but that one is probably good in that regard. Notably, I'd like just a touch more caster/trail on my Dahon.

That's quite the collection of bikes you're getting. The Liberte is a good deal, but I think the Bull even better, currently listed online at $499, down from $699 list. Add a double crank (for crank and bearings, derailleur, shifter, cables, I think you could do for $150 easy, if you get the crank deal I did), and that is one damned fine bike for $650. Seriously.

Mid-drive: A similarly equipped Dahon with mid-drive is about $2700, plus it's lame on motor power and battery size. I think with retrofit, you need one chainring to transfer power from the motor(?); Hopefully you can do that with the inner ring on a triple, so you still have a 50/34 for pedaling. On my bike, a triple would not have worked, the innermost ring was too far in for the derailleur, and if I had used a super-wide bottom bracket axle, the chainline would have been way off. But an innermost ring overlapping the bottom bracket, that should not be a problem as a mid-drive chain to the motor, if the motor is properly positioned.