i just bought a couple of the RVtoys bags. cheap and they seem strongly made. too big, really, for the bikes, but i suppose you could sort of strap it down in places to compress it. it does have backpack straps, but, probably won't be carrying that way on mass transportation. but we'll be in italy in a few days, and i'll let you know.
the BIG problem with the bags though is the smell. They smell SO bad. i understand the materials are new and the dying of the fabric or whatever, but geez...