Given any make will largely spend its time lurking in the boot or similar, does it need to be that expensive?
I've got one, an Audew brand with some nice features, used it a few times on my Touareg in Greece but never needed here. A quick flick on Google shows me a Noco Genuis which looks great value and doubles up as a trickle charger it seems, it could usurp the CTEK? no mention that I could see though of engine capacity as noted by numerous others, around £50 it seems .
https://www.amazon.co.uk/NOCO-GENIUS2UK ... 1830196582
Alternative is another Audew, though thats £70 ish and like the one I have which is kept in my wife's car, that car has a recent new battery but these things are insurance aren't they, pretty much guarantee on the day one would be needed it will be in the other car.