For Christmas I got a new drip tray and money to buy a new CO2 tank. I was looking at Micromatic and saw a 20# Aluminum for $115 and a 15# Steel one for $89. Is there a big advantage of one over the other other than 5# of CO2? I am cheap but I can be convinced to spend the extra $25 is there is a good reason. Is there a better source out there for tanks?