Nice to see a thread, where once, we all seem to agree about something! Yep, the Mintlp Protractor is superb, no doubt about it.
The TB Protractor isn't bad, but everybody seems to note differences in alignment when comparing the two, so with that said, I then wonder, is it the inaccuracy of the Sight Line TB versus the Arc Tractor, or is the TB Tractor in error some other way?
I wonder, and have asked this before, about some of these Arms, with "odd" null points, and can Yip then provide some custom Tractor per given Arm which seems to "stray" from other well known geometries? (Stevenson-Baerwald-Loefgren)
As others may know, there's another available Arc Tractor available, by Ken Willis, looks to be a very good quality as well, but is not a mirror, so the Parallax aid in aligning Cantilever may not be as good.
Still, on this Arc Tractor that he makes, one can have all three of the mentioned geometries above on one Tractor. Of course, being an Arc Tractor, it is only good for one known Spindle-Pivot Arm distance. Mark