For several years now I have been using Magisk development builds on all of my devices and it is a much better solution than Supersu. I do have a stock TWRP backup of the stock that you need to use Magisk, v1.1.1 but have never uploaded it
I am uploading it now, as you need it to use the systemless Magisk solution. You would need to download it, flash it in TWRP, then immediately flash the latest Magisk.zip in TWRP, to root it. Magisk is terrific. I have the latest cutting edge, canary and Unofficial builds on all 5 versions of my tablets.
If you need just basic root, the SuperSu that I have preinstalled in the AFH, v1.1.1 will probably work for you, However, Magisk will allow you to install various modules to add many additional features to the tablet.
I am now uploading it to AFH. It must be unzipped and place in the proper file hierarchy on your external SD card for TWRP to recognized it: /TWRP/BACKUPS/NX16A8116K/2017-07-02--16-09-14_V1.1.1.MMB29M.20161203.041025/(all of the backup files inside of this nested folder.) also copy the latest Magisk.zip to the MicroSDCard., Don't unzip it. By that I mean the root of the MicroSDCard, not the TWRP folder.
Boot to TWRP, click the restore button, click the select storage option at the bottom, select Micro SDCard, then Select the folder: 2017-07-02--16-09-14_V1.1.1.MMB29M.20161203.041025, then swipe to restore. It will take several minutes to restore.
After restore is complete and before rebooting, go back to the TWRP main page, click the install button and select the Magisk.zip, or what ever it is currently named, select it and again swipe to flash it.
You should see a message that it successfully patched and flash the patched boot.img with no errors.. After a success message, click on the reboot button at the bottom of the TWRP window, to reboot to Android.
The first boot may take several minutes to complete, as a new, unencrypted data partition will be created. In other words, it will be stuck on the Nextbook boot animation for some time, (several minutes), before it boots to the Android setup screen. Finally, setup Android as normal.
The Android File host upload is painfully slow. It is a 1.2 GB file and the upload sometimes fails. I may not know if it was successful, or not, until I get up hours later. If it fails, I will try again. It is at 69% uploaded, now, so I hope it completes.
All of my uploads are here, including the TWRP.img file. you must also unzip it also to flash it in bootloader mode with fastboot, copied to your PC. I copy it to the adb folder or platform tools folder, depending on how you installed adb and fastboot in WIndows. I however have a Linux Mint install. also, so I do it from there :
The Magisk Stable zip is here:
SuperSu development is dead, so I would suggest using Magisk, as it is constantly being developed.
My rom has the stock recovery and data removed so TWRP will not be overwritten if you flashed it and a new, enencrypted data partition can be created on first boot,after flashing it and Magisk.
The upload failed, I am starting again then going to bed. Hopefully it completes this time.
Here is the new download link: