Am contemplating a move to cylinder ownership instead of renting due to my sporadic use ie I can go through a bottle in 2 months and then be 12 months or more before I need another fill. The bottle ownership seems to suit me even with the relatively high cost of fills vs BOC etc. However, I am also keen to weld ally and stainless so that means 2 bottles. The CO2 bottles seem cheaper (6.8kg) and I could then have a CO2 bottle and a straight argon bottle for ally etc. So am wondering just how much of a difference I will notice between Argoshield and CO2 when welding mild steel. I generally weld nothing less than 2mm mild and use a Unimig 250 with .9mm wire.