There is more than one way to skin a cat, especially when that cat needs skinning very seldom (or maybe only once) in the life of your mill. Purchasing a reference that is an order of magnitude higher in both precision and in price in comparison to your no-name angle plate is not always the way to go when a bit of fiddling and care with your angle plate can produce the same result.
The big problem comes when you find your x/y is not perpendicular to the degree you had hoped, sometimes it can be best not to know.
Phil