I'm on this boat!
It depends on the tanks of course. I have three Protank 3 tanks; one of which is unopened in original packaging in a drawer in case I lose one. I have different flavors in each of my tanks.
The key to my setup is that I have a cache of replacement coils. About 50-75. I'm not worried about a tank going bad cause I have a back up that will likely last me 6 months or more as well as my second tank already in use.
Yes, this is what I consider prudent, cost effective and just plain takes the stress out of wondering what might fail or break.
