I got a Nexus 5X on 2016-05-10 (from Highend Electronics via Amazon.de, 323.80€ plus 9.99€ early morning shipping) with 32G storage.

Included is only a USB-C charger and cable, so I needed to get a USB-A-to-USB-C cable (Schwanthaler, 1m 8€), which was hard to find in a store.

Unlocking the bootloader

Quite similar to the Nexus 5. Again, this will wipe all data so do I as the very first thing (I did a OTA update to 6.0.1 first, tho).

I used android-tools-5.1.1r13 on Void Linux (Android Debug Bridge version 1.0.32).

• Settings -> About -> Tap “Build Number” seven times
• Settings -> Developer -> OEM unlocking -> Enable
• Settings -> Developer -> USB debugging -> Enable
• Plug in USB -> Allow

• Verify USB connection works:

  % sudo adb devices
  List of devices attached 
  00xxxxxxxxxxxx69    device
  

• Reboot phone, press Power then quickly Volume Down to enter fastboot.

  % sudo fastboot devices
  00xxxxxxxxxxxx69    fastboot
  % sudo fastboot oem unlock
  ...
  OKAY [ 15.398s]
  finished. total time: 15.398s
  

  (Choose yes on display.)

• Reboot, it now shows a spooky warning message and an open lock.

Rooting

• Enable USB debugging again and copy SuperSU:

  adb push BETA-SuperSU-v2.67-20160121175247.zip /sdcard/
  

• Reboot, enter fast boot and temporarily(!) load TWRP (I prefer to keep the default bootloader, YMMV) and install SuperSU.

  fastboot boot ~/tmp/twrp-3.0.2-0-bullhead.img
  

• Most steps taken from http://www.makeuseof.com/tag/root-nexus-6p-5x/

Install AdAway

You can now install AdAway.

Death

The phone broke on 2017-09-19, showing symptoms of what is known as a popular boot loop bug, even if it doesn’t actually loop.

I tried the alternative kernels from https://www.xda-developers.com/nexus-5x-bootloop-fix-boot-phone/ but I couldn’t run the phone for more than three minutes.