With the upcoming Mars opposition, and Jupiter rising, and Saturn, and the moon to observe at home, I thought I would take the plunge and get a pair of binoviewers. After running the math and finding I could use it on both the 12.5-inch and 20-inch, I found a good used pair locally and picked them up a couple weeks ago. I tested a few eyepieces on them to make sure I could reach focus. Then I bought a good pair of 10mm eyepieces. Tonight was the first to test them out on the 12.5-inch, on the moon, for an hour, through holes in clouds blowing through.
First impression is really, wow. The seeing was not at all good, but I felt I had very good resolution and I could see detail upon detail. Most noticeable was the color gradations and ray patterns were much more distinct. Craters seemed deeper; the terraced walls had angle and shape which they didn't have before. An mountains along the limb! Maybe it was the luck of the libration, but MAre Humboldtianum was very prominent and there were mountains beyond it.
So overall, very pleased. I didn't try the higher magnification configuration given the seeing (and my tiredness). I found focussing to be easy, even without diopters, and I could quickly find a merged image. I can't tell about collimation, but I didn't really notice any strain to my eyes and things seemed sharp. I could pick up Plato craterlet a, and hints of a couple others. So, I'm looking forward to more views!