It was invented for the Chromatone, a keyboard that eliminates black and white keys and treats all keys the same way, similar to a guitar fretboard. http://muto-method.com/en/index.html
Transposing then becomes easy because every scale has the same shape.
Thanks for that link, that is very interesting indeed. Being able to read the intervals more easily is certainly valuable, especially if you are playing on a chromatic keyboard.
However, I do like the fact that accidentals in traditional notation say something important: This note is out of the scale you are playing in. This is usually audibly very noticeable, so it makes sense to have it very noticeable in the score as well.
The three line system could be enhanced to show the notes that are in and out of the scale slightly differently, e.g. with color, or the size of the note-head. This would still have the benefit of being easily transposable.
It was invented for the Chromatone, a keyboard that eliminates black and white keys and treats all keys the same way, similar to a guitar fretboard. http://muto-method.com/en/index.html
Transposing then becomes easy because every scale has the same shape.