I just purchased quite a few Mint LP protractors to cover all of my turntable/tonearm combinations. The expenditure was significant but not nearly as significant as the performance increase attributable to them.
More importantly if the Mint LP protractors are correct, and I believe they are after listening, not a single manufacturer's protractor/jig supplied with their tonearm is accurate. Some are close but others are not.
The point is if you've invested in a decent table and tonearm, you'd be foolish not to spend another $100 or so and ensure proper alignment.
This device is a no brainer IMO.