Just returned from Andalucia Spain with a pair of Bike Fridays. First international trip (flying) with folders. Multi-modal travel is significantly easier with Bike Fridays vs. full size bikes and with suitcases versus bike boxes. Getting to/from airport is easier, hailing taxis and Ubers is easier, train stations and trains are easier, and small European hotel rooms and elevators are easier.
We hoteled, so we only carried two panniers each. We started and ended in the same hotel; they happily stored out suitcases for us.
We used the same panniers that we use on our 700c bikes and there was no issue at all. They handled pretty much like regular bikes on the paved and unpaved roads we explored. At no point in time did we think, "700c bikes would have been better here."
Based on our experience, bikes of all sizes are permitted on local trains. On mid-distance (MD or Media Distancia) trains, up to three bikes per train are allowed. They have three bike hooks in one of the cars for them and you need to pay for them when you purchase your ticket - 1 Euro per bike for trips of less than 100km, 3 Euro for longer. But as the guidebooks have said and in our personal experience, three is not a hard and fast rule. We ended up with four on our train and nobody cared. On the longer distance, high speed trains, the bike will need to be folded and put in a bag or box. We did not do that on this trip, but if we had to, we'd have to figure the smallest lightest bags that we'd have to carry with us for this purpose.
Some photos
Bike Friday All Packa with rear rack with Arkel panniers and and fork-mounted 4.1 liter Ortliebs
Bike Friday Pocket Crusoe with front rack and Ortlieb panniers
All Packa on local train. It wasn't busy so nobody cared. There seems to be a strong bike culture in many of the place we visited.
Pocket Crusoe on Media Distancia train. You can see how much more compact the bike is versus full size bikes.
Media Distancia trains officially are limited to three bikes. But here's the fourth.
All Packa and I squeezing into a tiny Spanish elevator.