Thanks everyone for the feedback.

Apparently, the Ritchey Breakaway is a bike that can be taken apart easily, while the S&S couplers are just a part that is used by bike makers. Is this correct?

So it looks like folding/break-away 26" bikes are really too big to carry on a train, and for a touring bike, you recommend I check 20" with suspension, à la Birdy, etc., or 24" models (Airnimal, Dahon and Tern).

I didn't find the Cadenza (Alfine 8) on Dahon's site. Maybe it was part of their catalog before the split.

I guess an option could be:

• a regular 26" for the city, with mudguards and front/rear-racks and paniers
• a folding/breakaway bike, either 20" or 24" for touring, ideally with light rear-guard that I can easily remove and pack

----
Edit: Apparently, this is the S&S page that explains what it is:
www.sandsmachine.com