Would the Starizona "Night Owl" reducer have any advantage for visual astronomy? I already have the Celestron 0.7x Reducer, which brings the EdgeHD 8" down to f/7 with 105mm back focus. The Starizona would reduce down to f/4 with 34mm back focus.
There is a limit to the width of the field that an SCT can provide.
A while ago, I exchanged email with Dean at Starizona regarding their large format SCT corrector for visual use with my C14. He was adamant that it was not appropriate for visual use. In particular, with a wide field eyepiece, it would make the shadow of the secondary mirror visible. He must have felt pretty strongly about it, because when I told him that I was also considering it for imaging and asked a few more questions, he never responded.
I will note that I have used a Celestron F/6.3 reducer corrector with my C14 and a Panoptic 41. It clearly shows both of the issues that he was describing. I have to imagine that an F/4 reducer would make all of this even more obvious.
My thoughts on this for visual is that you might get some benefit from the correction, but for increasing the field of view, you are better off at the telescope's native focal length with a long focal length eyepiece.
If you really want an F/4 visual instrument, my suggestion would be to look at a Newt.