Thanks Peaky :-) A good point. I've seen those lighter style AR glasses, which could be another idea, but I want to use the thing for keeping fit too.
I dug into the Quest 3 a bit more since posting.
Seems there's some conflicting reports on the passthrough quality, with some people reporting good enough to read a book, and others saying it's not. Some people are putting that down to poor lighting, and others saying that it's actually inconsistent build quality on the external lenses.

Originally Posted by Peaky:
Assuming dual monitors means working rather than gaming i am pretty sure you'll conclude the answer is no... even with a Vision Pro (which i borrowed for a few days) it isn't viable as the thing feels much heavier when you are just keeping still, and in real world use not nearly as sharp as a monitor. And it ends up pretty disorientating as the stuff in your peripheral vision (e.g. the other virtual monitor) doesn't feel the same as real peripheral vision.