[Wavytone]

IMHO it’s one more thing for those with OCD to obsess about. Unless you have a test lab most of us have no way to measure these things quantitatively and you take pot luck with what you buy.

Most have no means of adjustment beyond inserting shims under one side or another, ie trial and error. You’re more likely to degrade the mirror or prism by futzing with it than actually achieve much.

As Bojan said I don’t see it as a big issue for visual observing.

If it really bothers you go buy a better quality one from the likes of Lumicon, AP, APM or Televue.

BTW There was a report recently somewhere where a lab tested a large sample of diagonals to measure their orthogonality, transmission, wavefront error and other parameters. Misalignment is not the major problem.