bags are great. Miele say they have prototyped bagless cleaners but could not make them to perform as well as their bagged vacs.
the new multi-layered synthetic fleecy bags are better for collecting fine dust and maintaining suction than the old brown paper bags, plus they are much cleaner to handle and bin (the Miele ones have a flap that closes them to prevent spillage when you take them out of the machine) and animal hair, in particular, packs down tight into the bag so it holds a lot before being full.
If you check the spec for the cat and dog, I think you will find it has an activated charcoal filter to absorb doggy smells. You can buy the filter as accessory for other versions, but it is about £25
The Cat and Dog models (not all the others though) have the turbo brush which is about £60 if bought as an accessory. When I looked JL had a different model at £250 with £50 cashback which looked a good buy.
As far as I can make out, C1 is the small one, C2 medium, and C3 the large. The C3 has push-button power adjustment, not the turning knob. The larger ones have greater dust capacity.
John Lewis and Currys seem to be the same price at the moment. Debenhams were offering last year's blue model (a best buy) at reduced price; but twice they sent me the wrong model, and now it shows out of stock, so I have now ordered a black one at JL.