Although I'm an avid saver/repairer of inner tubes I have always binned ones where I have used one of these things, which tbh is only once.
I always carry one when out on my Brompton because I'm paranoid about the amount of faff required to remove the rear wheel (it's a 6 speed so hub gear and chain tensioner thingy). But I've never needed it ... yet.
Only had one puncture on my Brompton, I just folded up the bike and got the bus home