Lung Building Devices?

[[old] Marveller]

I was wondering what you opinion are on these powerlung, lung builder devices. i have a friend who has been using one and he says it helps him. what is your take on these things. I'm a little skeptical of them , but i have never tried one. If they do work which ones are good because i looked at them and there are tons of them out on the market. anybody's personal success and failures with the devices?<br />JR