Doc:
I hopefully would never need it. I believe most warm water "recreational" divers don't use them. Sometimes I think about it, though. I wouldn't take it unless I intended to use it.
Occasionally I read some story about someone whose "instabuddy" takes off or is otherwise hopeless, leaving you with no backup air source and I wonder then if carrying an extra air source would be wise. Maybe not, I have read the differing opinions on this and am not yet sure of my conclusion.
I didn't want to start up the whole pony argument, and was just curious if those who have traveled with the things have found that one size travels "well" and others don't, etc. I specifically avoided the whole issue of what size is adequate or if they are even a good idea. I have read those threads, and that information will factor into whatever decision I might make in the future, but didn't find much about traveling with them.
You are right about "cost vs. utility" but life is full of compromises and this might be one. Perhaps my question is silly, and I'll regret even asking, but I thought perhaps some folks had gone down this path and had first-hand information and insight about the ease of traveling with these smaller cylinders.
The point of your comments is well-taken.
Edited to add: I realize that my plans for relatively shallow and unchallenging diving would not seem to suggest that redundant air is even necessary. I know about the argument that good air management skills should make them unnecessary, the low rate of gauge failures, first stage failures, etc. I am just curious about the ease of travel with these things for those that do believe in them.
