I recently acquired one A-25 Zeiss Abbe Ortho, and I was so impressed that I began searching for another one for my binocular viewer. Finallly, after searching diligently in the US and in Germany, I found one person who had a pair of the A-25's and he agreed to sell them to me, but only if I bought both of them from him so I now have 3.
Previous to this time, I was using the Naglers and Radian with my AP155 and Stowaway, which I was happy with. But in a direct comparison, the ZAO was noticably brighter to me. Also, in the Nagler the last part of the fov near the edge was not completely in focus when the center was in focus, and I also found this to be true of the Radians to a lesser extent. I have always thought that the Naglers and Radians were colorless, but they were not when directly compared to the ZAO which were perfectly clear and colorless. Finally, the sharpness where the observing object is next to a lighter or darker object, I found that in the ZAO's the dividing part where the shades were different was noticably sharper .
I did pay a lot to buy the pair, and would like to sell the A-25 for $700 and this would include shipping and insurance. The A-25 comes with both end caps.
As a final note, I have looked through all of the ZAO's and the A-25 was my favorite. On some of the other ZAO's the eye relief is restricted, and even with the A-16 I could not view comfortably with my glasses on. The A-25 is completely comfortable when wearing glasses. The A-25 does have an extendable eyepiece shield that I found very helpful w/o glasses on since it did block out alot of stray light. Also, some of the other ZAO's have a smaller lens viewing surface, and the lens that you look through on the A-25 is very large, and I measured the lens that you look through to be almost 7/8".