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In the past I've had a good WO 2" diagonal, a good 1.25" diagonal, a medium 1.25" diagonal and a very cheap 1.25" diagonal (you tend to collect them after a while).
In terms of quality and engineering skill the WO is easily the best made of all of them. It has that WOW factor, and while the good 1.25 was of similar materials it just didnt look as good.
In terms of performance I was certainly hard pushed to see much difference between the best and worst. At least for visual observing they all performed well, maybe for imaging you can see the difference, but not visually (and I am reasonably experienced, over 10 years observing).
I also thing alignment is an interesting topic. I dont see the point of the arguement about the casing, and alignment. You dont align to the casing, you align to the optical path, so while being aligned to the casing might help it wont be right. All diagonals, by their design, wont sit flush when in a focuser, tighten the locking screws (in the focuser) and they all move a fraction, tightening the locking screws on the eyepiece and they move again, if you then add the 1.25" adapter you again get movement. While none of it is huge, and is generally ignored, it all plays up on alignment. If you are buying something that is 99% reflective you probably get more value playing with this alignment than anything else. Interestingly though none of my good diagonals alowed you to align them... the cheap ones did (but I never bothered).
For me one of the big advantages of the WO over the others was that it had a beveled edge cut into it, so that if the focuser locking screw came loose it didnt slide right out and hit the ground. Most of my others didnt have this and after having one hit the ground on a cold night I ended up getting them cut into them. That said having it added cost about $5, so not worth the extra $100 to have it.
For me, and this is just my personal opinion, I think the question should be asked why 2"? When I bought my WO 2" I assumed it would give amazing views and huge improvement, and that I would amass a number of 2" eyepieces. Well the image was no real improvement, and as I already had good/vgood eyepieces in the 1.25" variety I never did get many good 2" ones. So I was continually stuffing around with the 1.25" adapter, and on the occasion I did use a 2" ep having to remove it and then find it again later. In the end I would the whole 2" diagonal a bit of a gimic rather than a good add on. Most high quality low focal length eyepieces are 1.25", and when talking about long focal length going much over 30-35mm is wasted due to the puple size (from memory its a limiting factor) so the useable rang eof the 2" ep over the 1.25 is from 25mm-35mm, or generaly 1 ep.
But that was just my experience, everyone is different, and certainly the WO will make you smile whenever you see it, and soon forget about the cost. Also remember the WOW factor, lots of people will go "Wow a WO diagonal" but you will wait a long time before anyone goes "Wow a Bintel diagonal".
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