We're working out what we think - we'll add our view here!
Mountain Equipment says:
If you want the lightest bag we make to help free up space on your global travels then this is it. Perfect for short excursions when a comfortable guest house isn’t always guaranteed.
*Mountain Equipment use their own 'Good Nights Sleep Guaranteed' rating which they believe is a more accurate number for some sleeping bags and is based not just on the EN test results but on lab testing, their own use, thermal imaging and cold chamber work, along with a lot of data analysis.