Cooking with tins?

As an aside, I was appalled to discover that the fridge freezer my mum bought in 2020 was less efficient than the one we bought a decade previously 

Is that going by the efficiency rating listed on the label? They changed the rating system in the UK in 2021, getting rid of the A+++/A++/A+ to D system and replacing it with A to G. Now an appliance which was A+++ will be a B or C. Most freezers are now E or F, with some better ones at C or D, and a few much more expensive ones at A.