Is it against TOS to use this tool?

[Seddrinth]

ok I guess it's 'ok' to use as gm won't do anything to players using that zoom tool

if you don't let anyone know then you probably are ok

[moshev]

Well, it would be trivial for Square to detect you're using it - just check the FOV and max zoom values in memory now and then, and if they're different from the defaults, ban. No need to scan for the tool running, as it literally changes values in memory, which is technically a form of hacking.
That said, I think Square should just give us a FOV slider and allow slightly farther zoom. Even competitive FPS games like Overwatch and Halo let people select what is comfortable for them. I don't see people with 100 FOV having an advantage over people with 70 FOV in PVP, it's all a matter of what is comfortable for you. You can also always track enemies on the minimap. I also haven't heard of anyone advocating zoom hack's use to gain an edge.
I don't play PVP, for me it's all about comfort. The default FOV is too small and I can't see as much of the world as I'm used to. It makes it easier to also see all the cool boss animations when you're right up their butt, too.