Never ridden one, but the WeightWeenies Crux riders say the frame tubes give it kind of a smooth ride feel vs some other high-end options.
Building one up to suit with certain components 2x, you'd hit 17lb no probs.
Specs mention a 47/48mm max, but you might be able to fit a little more in the fork? e.g. 2.1.
To cut down tyre weight a bit, for the descents grip [fork] you could do something like a ReneHerse 48mm knobby EL, or a RocketRon liteskin 2.1.
48mm rear option could be a FuriousFred AddixSpeed [they measure closer to 48mm] if you're not doing a lot of steep+loose climbing.
I do like the 29x2.2 clearance on the kind of racy geo Lauf rigid as it opens up some big lighter-weight grippy tyre options, but the chainstay design sees it only 1x unfortunately.