I've flown once with a dedicated soft sided bag, but mostly, maybe 10-15 times, with a CTC bag or just a plastic sheet duct taped up. From memory the soft bag needs a fair bit more dismantling - the wheels and bars have to come off. Also you're lumbered with quite a large lump of bag, which may or may not be a problem depending what you're plans are. I guess they do at least have some protection. Plastic bags/sheets have no protection but, as the argument goes, the handler can see what they're dealing with. I did come off a BA flight with the bike snapped at rear dropout tho, so breakages do happen...not that it'd stop me flying again or using a plastic sheet.