Had Zenfone3 Zoom (ZE553KL), Miracast works fine, never test the android auto though. And due to software limitation of 2.4GHz Wifi band only, Miracast some times lag if you cast and stream at the same time. Asus phone tend to find some nice niche and value in the market, however being a non mainstream vendor you have to suck up the usual potential compromise such as lack of poor aftersale support, buggy/EOL firmware update, lack of 3rd party ROMs, etc.
The phone built quality is okay by itself, however it not a 'strong and solid' build where it can sustain some heavy abuse of use such as dropping at a rough surface (what happened to my ZE553KL). The ZenUI ROM is relatively clean compare to your typical Samsung and Huawei, camera is good for it price range and it stops pretty much at that. If you aren't really a 'root' and know what I'm doing in Android person with a heavy daily drive, I'll not recommend Asus as a phone choice.