Used mine mostly for camping (Whisperlite) and just being prepared if needed. I get asked all the time about it under there and share the thought process. I have a penchant of pushing my tanks limit. And since I have a dirt background, it made sense, at least to me, to be prepared.
I've carried this bottle since about the second year of owning the bike. So that's about 50,000 miles. No explosions, no issues with setting the bag down - I don't really take them off. Never in the way when cranked over or when doing maintenance. No problems with expansion or stale gas. But I do rotate the fuel occasionally. Usually just dump it in the tank or in the lawn tractor and fill with fresh 93 octane.
Mike