That's pretty cool! I'm under the belief that they can't (won't??) come to my place to fill the 100# tanks because they need a scale.
I might add, I've NEVER seen anyone use a scale when I schlep the tanks to the co-op to get filled
they probably don't want to fiddle with small tanks like that!
(wouldn't blame them either)
The co-ops here have mobile filling for small tanks or they just exchange the 100# "pigs". Either way comes at a charge wether transparent or built into the price of the gas.