That looks surprisingly good for me in Firefox, but from my experiments making these tricks work in production, browser standardization is a long way from the point where we can do this at arbitrary sizes in the real world.

The problem, more than anything, is the way these css-only triangles get aliased. Since they're a side-effect of rendering borders, they never get properly anti-aliased the way fonts and shape edges do, and as a result the edges end up jagged at certain sizes and color combinations.