Had poor seeing tonight, but pulled out the ADC to try again with the 110ED. It was disappointing. I agree it is finicky, and more importantly, can be rather impractical. I haven't tried Barlowing before the diagonal to some crazy high focal length & ratio for the contraption...I would have to drift time to work out the effective focal length.
I played with it awhile getting it dialed in for Jupiter to get the sharpest image it would provide, adjusting, recentering, refocusing, repeat. The end result was less detail than without the ADC (both before and after.) But in poor seeing and with Jupiter at ~30 degrees, perhaps this is not a surprise. I think I had somewhat better results with it last year on Mars before the dust storm hit, but don't recall the particulars. I don't recall it degrading the image like this. Red filters dealt with both the atmospheric dispersion and-to some degree-the dust, so I had no reason to use the ADC later and forgot about it. Without it I could see that storm in Saturn's polar region with the 20", and that wasn't great seeing either.
The ZWO ADC won't work in the 20" f/5 and that blows away the scopes I have that it will work with, so it is of limited utility at my latitude. I would like to catch some good seeing in the backyard to give it a fair shot with a couple of other scopes though. I do expect it to have some benefit when the seeing is good. Better seeing makes it easier to tune the thing, and should allow it to actually improve over the base level conditions.
And again, the ADC would likely be of considerably more use to me at latitudes in the high 40's and above. It might be of use here as well if I was imaging (and could use that to better tune it) or had very good seeing to work with where the ADC would show noticeable improvement visually.