Asus products are bullet proof, even their cheapest zenfones do not feel cheap. My mom has a Zenfone 6 for over half a year now, it has a matte back, the bezels are larger than what i would like but in the hand it does not feel like any other android phones of the equivalent price.The other thing about all this spec in a yet untested phone, who knows how durable it will be? How does it perform in arid climates? Cold climates? How does it fair if dropped? Does it hold a wifi or data signal as you expect? Who knows but we are to quiver just because of spec? If it doesn't run WP 10 why worry?
I would say you cant find a more premium feeling device at that price point, the camera is MEH but its still better than the rubbish 5mp shooter in the 635. Thats why i recommended her the zenfone instead of the lumia 635.
We also have 3 Asus laptops and 1 desktop so far 0 problems from all of them. Only complaint i have is the speaker quality which is below average, other than that the phone looks and feels great. I would only imagine the successor to be better in almost every way.