Well, Mike, I had a set of ZAO-1's and still banging my head why did I sell them...well, the truth is that they helped me with a house downpayment...Anyways, without exception they all gave very clear, super sharp images. On the other hand, I love to observe DSO's with eyepieces that has a wider FOV, and I love my Panoptic, Delos and Pentax XW very much, they are all excellent eyepieces. It was especially the 16 and 25 mm ZAO's and the Pentax 20 mm XW when I had a kind of out-of -body experience during observation, when the Celestial OBJECT took my full attention and was not trying to reach for other eyepieces for a better viewing or to adjust and again adjust the focuser. This was a lamentation of ZAO's but other excellent eyepieces just do great job too...
Istar 228 mm f7.7 refractor on AP900 mount
Mike, I am like you. I have a difficult time "seeing the difference" when on axis. Any decent eyepiece will give a similar view when the object is in the center of the field. It is the edge of view that people chase. Once you get above 70 degrees, it starts to cost you a lot of money to have a perfect view in the entire FOV.