The cheapest way to find what your usage is going to be is to a rent free initially in my opinion. The Zolkszone is good if you use enough gas but if you are an occasional user it's very easy to end up 2-3 years down the line paying rental and never fill the bottle up. The other issue as an occasional user is the fact that you will often be working outside normal hours and you can bet your bottom dollar you'll run out on a Sunday morning. Many of the rent free stockists are at places like garages that are open 7 days a week, and you can also pick up a second bottle to have in reserve and return the empty one when you swap over and get your deposit back.