I've since got my replacement BST (Arcturus) binoviewer and have been experimenting with it this evening. The optical quality is very good with no obvious dimming in either side. I tried a 1.25" prism diagonal to shorten the lightpath enough to see if it would negate the need for barlows. The only eyepieces to focus (just), were the supplied 32mm. There just isn't enough infocus for any others and so barlows it is. The supplied 3x nosepiece barlow works quite well although the magnification is too high. It's very similar to a Revelation 2x barlow element screwed into the normal nosepiece, showing the 2x is very near 3x in this setup. The supplied 1.85x nosepiece shows a bad coma from about 50% from the centre view and so I didn't bother with it.
The seeing tonight wasn't great but with good transparency in a cloudless sky. The only target tonight was the moon which was bright and clear. All stereo views were with the 32mm eyepieces as I don't have any other pairs. The field of view was roughly similar to my BST 8mm eyepiece in mono. Starting with the Revelation barlow the view was extremely good. The lunar surface was more crisp and had greater contrast than I've ever seen with mono viewing. There was a very slight colour which was comparable to normal mono viewing with the 8mm. I tried the 3x nosepiece barlow expecting the view to be reasonably inferior as it was a cheap bundled device, but was surprised to see the colour shown with the Revelation was almost non existant and better than the mono eyepiece. The whole view seemed to be cleaner, with the Revelation view looking ever so slightly ivory in comparison. It did show a flatter field though with the bundled 3x showing a little spherical error about 5% from the edge of field. Both barlows had the uncomfortable result of putting the eye position further out than normal. This meant I had to hover over the eyepieces holding a critical alignment until my muscles started to ache. I would much rather be able to rest my eye sockets on the eyepieces so that my relative movement would be less. Eye positioning and IPD is quite critical.
The collimation was ok and I could immediately merge the lunar images successfully. It did need further adjustment as shown by the misaligned field stops. This was easily achieved by shifting the eyepieces while looking at fairly dim star. I'll have to do this probably everytime I use the binoviewer but like the fact I can easily adjust it to be pretty much perfect.
The 32mm eyepieces seem very good value for bundled items although the necessary barlows affect them too much. To get an idea what eyepieces might work better I tried 3 other BST eyepieces, 18, 12 and 8mm. These were put in the left side of the binoviewer as I only have one of each. The 18 and 12mm worked very well with the 8mm greatly dimming the view and not working at all well with the current seeing conditions. The eye placement with each was a lot more comfortable though. My thoughts are that a pair of 25mm BST's would be a good purchase, and another 18mm to form a pair. Later in the year when I've had a chance to try some planetary viewing it might be worth getting another 12mm. One thing I noticed is that the plane of focus for the BST eyepieces in the binoviewer is very close to the surface of the bottom element. If this has any dust then it looks like your eye has suddenly gained a lot of floaters.
I generally use binoculars more than anything and so I'm very pleased to be able to use two eyes on my scope too. This will only be for high magnification lunar and planetary views though as the widest view so far only shows around 75-80% of the lunar disk. I can obviously get a better wider view straight through without a barlow and diagonal which for me is too tortuous for serious consideration. There is the ED version of my scope available which has a removable tube section. This would give better views and allow the binoviewer to be used without a barlow which would be a lot more user friendly. I may keep an eye out on the used market.
This is my first proper viewing with this binoviewer and like the title of this post I couldn't be happier either. It's hard to believe such an improvement in viewing from this price.