I'm sure they work to some degree, but I just don't think you're going to convince anyone to go back to old technology, because it's less convenient and has other drawbacks. Market share is likely to hit parity between corded and cordless soon, with cordless dominating thereafter, especially when solid state batteries come out soon. Even if you go for a corded machine, independently verified data clearly shows Dyson's latest upright mains is the top performer with no running costs, so why someone wouldn't go for that one for the 'rest of your life given reasonable care' is anyone's guess.