I used these (after a very short wear-in period) in Knoydart and the Cairngorms in May. They proved to be warm, tough and completely waterproof (we had some serious rain and blizzards). They are comfortable enough for general walking (though I'd use a more flexible boot if there was no chance of snow) and worked very well in crampons and on snow slopes (the Grivel Air Tex New Matics fit them like a glove).
It's nice that they are genuine UK sizes, rather than UK approximations of EU sizes.
I've used Mantas on a winter skills course and when I was a mock-student on an MIC assessment - the Mantas are also very good and there is little between the two boots. Having slim feet, the Asolos fitted a little better and I was happier walking on the flat in them.
For long mountain walks when they are new, tape your heels with Zinc tape, as stiff boots will move on the heel unless cinched very tightly.