So we tried an Urban Arrow this morning. It's good, much nicer to ride that the Babboe. Wee man really enjoyed sitting in the box too.
Handling took a minute to get use to but rapidly got some confidence (tho not enough to do a rolling U-turn on the small streets we used to test). The brakes (hydraulic disc) were good even in the the wet.
Motor assist was pretty solid but I didn't try any big hills.
Returning to the disc v roller: seeing as we have some pretty steep hills of non-negligible length, so discs would be be better for that. We will have a garage so it won't be stored in the rain.