Re mezzo.
MEZZO D9 FOLDING BIKE UPGRADED TO 21 SPEED PLUS EXTRAS | eBay
There is a quick release rack system that works really well and there is a possibility of using the seat post and bars to carry addition luggage. The large commuter bag is really large. There are also compactable panniers but you would need to avoid heel strike. The mezzo rack is much bigger than the brompton version about 50 to 100 percent.
The curve is a small package. You will have no issues on a train. It's footprint is reduced if you stand it on its edge. it's a perfectly userable train commuter.