I've got a safefill gas bottle, which holds 15 litres, I think it's the equivalent of a 7kg calor bottle. I've only been using it a couple of weeks, but it doesn't last very long, it was full on Monday, and now there is 1/4 left after 3.5 days work. That is supplying hot water to 2 reels @ 40 deg.
I don't know if that is how much everyone uses or not, but I was hoping that the bottle would last longer than that.
I would also be interested to hear how much others are using.