It seems the shader transparent version is badly aliased? The effect is less noticeable on Chrome than Firefox, but it is still quite visible. This defeats the purpose of vector graphics...

It's a nice trick to play around, but that limits its usefulness.

It is indeed badly aliased. The technique demonstrated does not take into account antialiasing in the initial render, which causes this issue. There are ways to improve it, but I would advise against this approach in general since it doesn't handle these edge cases well.