From experience with a set of Dunlop M2s you would get about 25-30k miles out of a set of winter tires if you keep them on in the summer and provided you cover equal miles in summer and winter.

I doubt very much that the Nokian would do better than that but if you go ahead with it I'd love to hear how it works out. I am a big fan of winter tires as summer tires and all-seasons tires are madness in a climate where ice and snow occurs. I find it hard to imagine that Nokian found the silver bullet to that as W/T are always softer so that they can grip in cold temps. So, let us know.

(I frankly can't believe my X-Ice have held up as well as they have, over 30k on them by now and still a few thousand more in them).