I can already do all the things you describe. I can tune a guitar totally by ear, without playing any extra notes, and I'm not worried if its 440 or not, as long as it's in tune with itself.
I know all about intervals and do quite a bit of SATB arranging.
I have to be able to find notes quickly with 30 or 40 singers in front of me. I can do this with a tuning fork.
I'm just wondering if it's really possible to learn like the website says.
Then I could direct a choir with no tuning fork!