Meh, I pity the paranoids, and sympathize, more than worry about them. It's the ones marketing this kind of paranoia I don't want to know. They're selling something that IF it's needed they won't get to enjoy their money, and IF it's not needed then the buyer get's nothing... well, maybe a little peace of mind. A very little since they still have to believe in some kind of doomsday scenario to justify the purchase, and worry about making it to the shelter in time, and the whole "what now" thing for after that.
It's like anything else; how much do you need it and how often are you going to use it? Stuff like this though really baffles me.
I mean, suppose you bought one. How would you keep yourself supplied after the "big one" hit? And if you invited friends and family for safety, then how would you provide for them? And what would you do while down there? Play cards or watch DVDs all the time? I mean... dang. How long do you stay down there? How do you know when to surface?
I don't know. It's like the high end equivalent of tin-foil hats or an AK-47.