Feel free to post here or in the comments of the gist what issues you've encountered, maybe there's something we can improve. The guide is not perfect, I spotted multiple things that would require more precision already, but so far was too lazy to update it thoroughly. However I did multiple backups and restorations over the week-end and can confirm it works, you can even restore a backup from one Pro¹ to another Pro¹ if you rename the TWRP folder to match the name of the second Pro¹ (using "fastboot devices" to get its name).

It's possible that the issue you've encountered was with backing up the hybris-boot.img, and couldn't go further. There was a change in the permissions of this file over later updates and it couldn't be backed up the way it was initially written in the guide; that part has been updated now.