I have a Canadian-made SoloRock 16" all-aluminum folder and like it wuite a bit. I ordered the 3-speed internal hub option which is unfortunately an SRAM hub and I'm not particularly fond of it and wish it were a Sturmy-Archer or Shimano S3 hub instead, maybe with a coaster brake to eliminate a cable going back. For that matter an old Torpedo automatic 2-speed hub or Bosch kickback coaster brake hub would be nice too.
I've been keeping my eyes out at used bike breaker shops for a suitable hub which I can rebuild
into a new 16" rim.
I used to own and operate a small hobby bike shop back before we went cruising full time and specialized in vintage bikes -especially British-built Nottingham Ralieghs. I amma big fan of the Sturmy-Archer 3-speed IGH and can completely rebuild
one with my eyes closed practically.
A derailleur on a folding bike is sheer folly on a boat
where the bike is getting tossed around in a travel bag. The slightest pressure on the derailleur will tweek the derailleur hanger which will invariably ruin smooth and precise shifting. Transporting such a bike in a dinghy
and loading it in an out of boats and docks is a surefire way to tweek a derailleur hanger. An IGH is a no-brainer IMHO.