[ZTE Axon 7 ROMs, Kernels, Recoveries, & Other Deve] Controllerboy:
Okay, so I tried the tool. Here are my steps.

0) I started with an A2017G with locked bootloader, no root, stock version of B03 running on it.

1) On the phone, tap the build number to enable the developer options

2) On the phone, enable OEM unlock

3) On the phone, enable debugging

4) On the PC, download fresh portable version of minimal adb and fastboot, unzip and add folder to root of hard disk

5) On the PC, download TWRP version for A2017U, rename to "recovery.img", put in same folder as adb.exe

5bis) On the PC, I also copied the recovery.img file in the adb folder and renamed that copy to recovery.bin. I was not sure which of these two files the axon7tool was going to use, so I made sure they were both present.

6) On the PC, download axon7tool file, rename to "axon7tool.exe", put in same folder as adb.exe

7) Phone + PC, connect phone to computer via USB

8) On the PC, shift + right click to open command in adb.exe folder

9) On the PC, enter command "Adb devices"

9bis) On the PC, it should show one device with a code

10) On the PC, enter command "Adb reboot edl"

11) On the PC, open device manager and verify that the phone is detected as "....BULK" (don't remember the exact name)

12) On the PC, enter command "axon7tool -r gpt"

13) Phone + PC, after it is executed, phone reboots.

14) On the PC, enter command "adb reboot edl"

15) On the PC, enter command "axon7tool -r recovery"

16) Phone + PC, after it is executed, phone reboots

17) On the PC, enter command "adb reboot edl"

18) On the PC, enter command "axon7tool -r boot"

19) Phone + PC, after it is executed, phone reboots

20) On the PC, enter command "adb reboot edl"

21) On the PC, verify you now have 3 backup files in your ADB folder for gpt, recovery and boot

22) On the PC, enter command "axon7tool -w recovery"

23) On the PC, wait till it finishes

24) On the phone, your phone should reboot

25) On the phone, shut down your phone and boot it to TWRP by holding both the power and volume up button

26) Enjoy TWRP

A) You may notice I did not use the Zadig steps. Doing so resulted in axon7tool not recognising my phone anymore (it just disconnected). I think as long as your phone is recognised as "....BULK" it's in the correct to use the tool.

B) You may notice I enabled OEM Unlock and Debugging in the Developer options. I'm not sure the OEM Unlock part is needed, but I am very sure the debugging setting is needed. If you don't enable this, your phone will never be in ADB mode and you can't execute adb commands.

C) After opening TWRP, I did something stupid. I FORGOT to backup my system. DO NOT FORGET THIS, IT IS STUPID to do so. I had copied google ARM64 apps and Cyanogenmod 13 by UnjustifiedDev to my MicroSD card, flashed it, and my phone wouldn't boot anymore. If I had been smarter and made a copy, I could've just restored my backup via TWRP. Now I was stuck with a phone which didn't boot into anything else than TWRP.

D) Because I had been a dumbass, I had to restore my phone to working order by flashing the TWRP-Flashable B06 Update with the B06 Bootstack. created by DrakenFX. Unlike stated in his thread, flashing this (on a locked bootloader with TWRP recovery) DID NOT ERASE TWRP and/or replace it with the Custom recovery. I'm not sure why, but think the fact that I ticked "OEM Unlock" before doing all of this + the fact that when entering TWRP, I gave it permission to modify system partitions (it asks you the first time you boot into TWRP, saying that otherwise, phone updates can erase TWRP itself) made the phone keep TWRP anyway.

So, after all these steps, I have an A2017G with locked bootloader, with TWRP and with the stock A2017G B06 update running on it.

My ultimate goal is to install Z.A.D. MIX Debloated Custom ROM but it seems you need to unlock your bootloader to do that. If I find a relatively safe way to do that, I might if it's the only way to get ZAD MIX. As stated, Cyanogenmod currently doesn't boot on my phone. When I get back from work, I'll try again.