iv checker

Because it's calculating potential level and IV combinations based off information provided by the game, just like all screencap based IV checkers.

The methods it uses to decipher the output in no way breaches the ToS.

Niantic do nothing about far more serious breaches of the ToS ( see apkbreakdown ).

Before anyone jumps to conclusions, I am happy Niantic are fine with it, the ToS is there to protect against more malicious intentions.

I'd like to flip the question: why do you think it is? What is the practical advantage it gives you that's unfair?

I dont use it, i rather check it manually using gamepress iv calculator if i think i've got a good one from appraisal.
But i dont mind trainer who using it, doesnt affect my gameplay at all

Like so many things that people get annoyed about, fist ask yourself how it actually affects you? Does it cause you any problems, or reduce your enjoyment of what you plan to do (in this case how you play PoGo)?

I have the app I think you're talking about, it's amazingly fast for iv checking and makes that part of the game much less dull and time consuming for me, but I don't use the new function you're talking about, simply because it serves me no purpose, I don't need to know before throwing what it might be.

You check your screen and input the Pokemon's status on a calculator, right?
The program checks your screen and input the Pokemon's status on a calculator as well, right?
How are those two different?
If, instead, you would take a screenshot and put just the screenshot into a program for scanning, would it be OK? Or would it be "cheating" as well?

It's not breaking the ToS, checking the game data you don't have access to, and it doesn't affect other players at all, so I don't see it as cheating.
(And no, I don't use that kind of program myself. I just go to online calculators.)