Which protractor and alignment tool is best for you depends on your needs. If you use one cartridge and arm and aren’t looking to change or experiment a custom paper or plastic protractor will work fine. You won’t be able to measure everything but you can get close and fine tune the rest of the way.
When I was a dealer I was mounting lots of different tonearms and cartridges and needed a variable gauge. I used the Feikert (still do) because it’s pretty much bulletproof (assuming you pack it back up in the box when not in use) and has survived moving from station to station around the shop and travelling to customer’s homes and audio shows. I’m not suggesting the Feikert is the best. But it’s worked well for me.