This is a very simplistic view of setup, you are assuming that the cantilever, diamond tip etc have been mounted correctly. In reality, this is never true so in that case this setup is wrong.
I don't agree. Cantilever has nothing to do with it. Cantilever is not even viewed in this approach. It is being ignored. Simply put, correct azimuth is achieved when the stylus is sitting perfectly vertical in the groove, and not tilted to either side, when viewed perfectly head-on.
To confirm this, you get eye level down on the LP and simply view the stylus directly head-on as it sits on the mirror. If the actual stylus and the reflected stylus form a perfect vertical line....you are there!! It is very easy to see when this verticality does not occur.
Not saying this approach yields "better results" than the high tech stuff you link. But I am willing to bet it gets you damn close....and possibly so close you won't hear any difference.
I agree that build quality is sometimes not perfect. But even in that case, this approach still reveals whether (or not) perfect stylus verticality is achieved.