jur

+1

The handling ie responsiveness/twitchiness of small-wheeled bikes differ widely:

I have a 20" Dahon/Yeah, (same as the Helios) and it is extremely light and responsive ie twitchy. But I can ride it hands-off.
My 20" Swift is less twitchy, but cannot be ridden hands-off, it veers all over.
My 16" Mini is less twitchy again, and I can ride it hands-off.
My 20" R20 is less again and can ride it comfortably hands-off. It's less twitchy than a light roadie.
My 20" Moulton is less twitchy again and I can ride it hands-off comfortably.
My 18" Birdy is least twitchy, heavier steering than a typical road bike, and I can't ride it hands-off at all.

I ride my folding bikes for all reasons: from short utility trips to commuting (50km round trip every day) to loaded touring to extra-long distance audax rides (brevets).

I know from experience that the ride experience from any bike comes from the whole bike, but it is very typical to find comments about small wheel bikes' harshness and twitchiness and unsuitableness for longish rides. None of these are true. If you are comfortable enough on a bike *any bike* to be in the saddle for 8h, then you can ride it anywhere. If a 700c bike fits poorly and has typical road geometry then you won't be doing any long rides on it.

Fit is paramount, wheel size almost irrelevant.