What for? These have been on the market for years as a twin rope, only recently certified as a half rope. I guess they occupy a similar niche to the Edelrid Apus 7.8, which I've used in the Alps and found great as a twin rope most of the time, switching to half rope technique for the odd zigzag pitch.
For permanent half rope use for UK trad I'd definitely want something beefier.
And you definitely need a belay device that's rated for skinny ropes, something like a Bugette of a MicroJul.
In reply to WillBroad: I've owned 8mm ropes in the past. Personally for that diameter and thinner I'd be looking to use the buggette. Larger cleated devices would probably be ok on moderate falls but on anything high factor I think you'd be asking for trouble. The manufacturers tend to be a bit optimistic on the range of ropes they say their devices can handle IMO.
I bought my 8mm ropes when I was doing a lot of summer / winter mountain stuff in scotland. Now I tend to crag more I went back to 8.5mm for added secrutiy, less stretch (but not much difference in max force) and more durability. One thing to bare in mind is running gear on one rope, I wouldn't be trusting doing this where a fall would very likely end in serious injury on a rope as thin as 7.5 mm if there is any chance it could rub against an edge across a short section or get cut. 8.5mm gives a lot more security in this regard.
Not used the Mammuts specifically, but I've got the Edelrid Apus 7.8s and my climbing partner has Tendon Ambition 7.8s, and we use BD ATC Guide/Petzl Reverso 3/WC VC Pro 2 with no problems at all, and they also work fine in guide mode. But as others have said, something beefier might be more suitable/durable.
If you're going to post that image it might be sensible to post the warning that goes with it:
"The biggest problem is that the manufacturers have not recommended this technique in their literature and hence we don’t know if there are any unintended consequences. So it is a use-at-your-own-risk approach, so test your device first somewhere safe and with a backup. It is important not the use the approach with any belay device that relies on the locker being forced into a slot or niche – i.e. an assisted device. (For example: the click-up, alpine-up, smart, jul, etc.)"