Best Alignment Protractor?

Now for a somewhat different opinion. The horizontal tracking angle (HTA) that you are setting with a protractor is the least important setting of all to get with absolute precision. It is incorrect most of the time as there can be at most two places where it is correct, that is, stylus tangent to the groove. Moreover there are several solutions about how to set HTA, each of which has its partisans. So this is not a setting to obsess over. More important is SRA and especially azimuth.

That being said, the $20 protractor sold by turntablebasics.com, used with care, will set HTA to the most popular setting as accurately as anything out there. Moreover it can be use with an arm of any length. The idea of spending big bucks for an HTA adjustment protractor seems unwise IMO.

Sorry, but there is no single "perfect theoretical alignment." There are several well known alignment schemes. They even have names, and some are promoted by tone arm manufacturers.

None of them is perfect, as the alignment of all of them is wrong almost all of the time.  The issue come down to where you want your mostly misalignments to be.

"'perfect theoretical alignment' to the scheme used by Mint" is, I'm afraid, an oxymoron.  There is so much misunderstanding about setting up cartridges that is only enhanced by such statements.

Mint probably uses one of the usual standards, Baerwald, Lofgren, Stevenson or whatever, but fails to note in its advertising what that standard is.  Reason enough IMO to stay away.  The popular ones have been known for at least three generations.  My guess is that they use the most popular one, Lofgren B.  It is used by most devices whether expensive or inexpensive.