Folding bikes... Collapsible is more of a spontaneous folder.
If I was running 20 inch, I would assume I was getting some benefit in efficiency from the smaller wheels, and I would spend some of that moving up the scale on either tire size or some sort of suspension effect to counter the wheels.
S&S is a good product, though there are other methods of achieving the same thing that are more frame buildy, VS the CNC approach taken by S&S. Rene Herse was a well respected french maker and had demountable bikes, as did others in France. Not sure who offers what, at what price currently.
http://www.43bikes.com/herse-demountable.html
http://www.cycles-alex-singer.fr/cat...o-camping.html
Yates and Bob Jackson in the UK make excellent bikes and handle S&S jobs.