and meNewer than me...
Unless Sealey has licenced the TARDIS technology then as far as welding time goes I don't believe you and I don't believe the Sealey catalogue either.
1kg of liquid co2 converts to 19.3 cubic feet at atmospheric pressure - or 546.5 litres.
At the 'normal' mig flow rate of 10 lpm, that'll be 54.65 minutes of welding time.
To get the 3 hours Sealey advertise, you'll need to run at 3 lpm, which simply doesn't work.
(I've slightly rounded a few numbers there, but in all honesty if you get a real actual hour out of one of those with sufficient shielding you're doing well.)
The chap that runs sgs is a member on forum.I really do like the idea of using fire extinguishers past their "use by date" but getting a regular supply of those might be quite tricky. I've been speaking to a chap at work who does welding on his car at home and he suggested a couple of nationwide rent free places in the uk. Has anyone had anyone had any experience with either of these? Personally I prefer the look of SGS gases since there is a local garage nearby that distribute their cylinders. Also *removed for legal reasons* seems to have a deposit which takes into account depreciation of the bottle over time :-/
http://www.sgsgases.co.uk/mig-tig-welding
https://www.*removed for legal reasons*.co.uk/