Seeing the cantilever from all angles is easy. I did not even have to use the magnifier. If you can see through to afford it, it is most definitely worth it. If you change cartridges frequently there is no better way to go.
I don’t like the mirror surface on any protractor, you will see not only reflections of the cartridge and cantilever, but also reflections of the alignment lines on the protractor. I put my VdH mirror protractor to the garbage. The reason to avoid the mirror surface is pretty obvious!
I never looked at the Feikert closely but the grids are vague. I know the SmarTractor is something like twice as expensive but it is vastly superior and intuitive.
Do not comment on something you never tried yourself.
Dr. Feickert NG is great for all my cartridges and tonearms. The build quality is superb! Actually if step-1 is correct then you’re done. If you can see a white lines on black surface you don’t need anything else except for the flashlight (provided with a Feickert protractor).
I don’t use a magnifying glass during the alignment process (never).