[Asus ZenFone 3 Deluxe Guides, News, & Discussion] asianflipboy:
Update Impressions

Happy to report that the update has improved my phone's performance. Before, when I would go to the gym, listening to Spotify via Bluetooth would drain the battery from 95%->60%. Post update, battery stayed above 80% from full charge. It also feels a bit faster overall. It's a bit too early to tell if it's for better or for worse, but right now I'm leaning towards better. Negative would be it reinstalls the bloatware, but after rerooting and using Titanium Backup, they were removed without issue.

If you're rooted with TWRP installed, I'll list the update procedure I did, since we don't get the OTA updates. I'm also writing it up just to have it for reference. I have the ZS570KL @ 2.15GHz so make sure if you're Pro(2.4GHz) you make adjustments. You'll also need a computer (I use Win10 but any computer with fastboot installed will work really) with fastboot in order to reflash TWRP.

Part 1: Returning to stock recovery and updating

1. Downloaded update from Here. 2.15GHz should be the second one down.

2. Downloaded stock recovery from Here. /u/Ryder. has pointed out the Zentalk forum has the latest recoveries available, so check there first. At the time of writing, I was pushed to login to view that forum, so instead I just grabbed the latest available from AndroidFileHost, 5.15.44.2562.

3. Move both to SD card. I don't think this might be necessary, but I know it works. I think stock recovery only reads off the SD card, but I can't recall. If you can't navigate to the files during the update, try doing this step.

4. Reboot into TWRP by turning the phone off, and then powering on while holding the Volume Down button.

5. In TWRP, hit Install, navigate to the SD card, and select the stock recovery. Swipe to flash it.

6. Reboot into recovery again. Once you see the ASUS logo, spam the volume keys. I had an issue where it would boot into a "No Command!" screen. Pressing the volume keys while it's loading up the recovery pushes it to load properly. If you get stuck in the "No Command" screen for more than 2 minutes, reboot by pressing and holding VolumeDown+Power buttons.

7. Once in stock recovery, select apply update, navigate to the update file and flash.

8. Reboot into updated firmware!

Part 2: Reinstalling TWRP

1. On your fastboot enabled computer, download TWRP 3.2.1* from Here. Rename the file something short to make it easier to flash (I renamed it to TWRP.img). *3.2.1 is available in the Mega. At the time of writing, I only checked the AndroidFileHost link and didn't check to see if there was an updated build for it. It is Oreo compatible, so when they finally get around to giving us Oreo, you'll have a suitable recovery to go along with it. :D Thanks to /u/Ryder. for the heads up.

2. Open a command window. Make sure you either move the file to the directory it opens to, or navigate to the folder it's in.

3. Put your phone into fastboot by shutting it down, then powering on while holding the volume up button. It should say FASTBOOT on the screen.

4. Plug phone into computer.

5. Run the command "fastboot flash recovery [TWRP.img]" where [TWRP.img] is whatever your file name is.

6. Reboot into recovery to test it!

Part 3: (Optional) Rooting your phone with Magisk

1. Download the Magisk Manager APK from Here. Only grab it from here, I don't think the PlayStore one is legitimate.

2. Open Magisk Manager, and hit install. It should prompt you to download Magisk 16. Hit install in the popup. Let it download.

3. Reboot into TWRP. Hit install, and navigate to the file (should be something like InternalStorage/MagiskManager/Magisk-v16.zip). Install it. Before rebooting, I recommend wiping Dalvik/Art and Cache.

4. Open Magisk Manager to check if it's installed. Enjoy root!

Hope this helps someone out there. With the infrequent, non-OTA updates, I have to remember how to do this every time I update. It's easier to have it written down for reference. :D