Does anyone mount two bottles so there is an extra when one runs out or do you just have Ann extra one on hand to make the change?
At this point in time I wouldn’t spend the extra money. Wait until you have run it a few times and see how long one bottle will last. Even then, I’d think long and hard about installing a second bottle. How often will you need to change it out, will you ever be in a position where you won’t have the time to make the swap? Maybe pick up a second bottle if you find a good deal, just check the date on it, some places won’t refill bottles unless they have been certified within a certain period of time.