As someone who's just been getting into photography (and just bought a really nice camera and an expensive Adobe RGB monitor for my desktop), I can't stand True Tone and have turned it off. I spend a long time tweaking the colors in my photos and I really like using the iPad for viewing photos, so I don't want the colors distorted. Night Shift is okay, because I don't mind it being yellowed for the brief time I use my iPad before bed. But True Tone, while good for people who don't care much about photography or graphics, isn't going to work for me.
Also, Night Shift is just one change at a designated time. But with TrueTone I was very aware that the screen was changing just while moving the iPad around my house, and that bugged me. It was like "hey, wasn't this more yellow a few minutes ago?"