Also, when the DK is completed I will try the coma corrector for visual use. And I will report the results back here to add to the knowledge base.
When I worked on the 16"DK (f/6.4 with a 40% obstruction btw) I was told by a professional optician that it would need a specially made corrector to suit that particular scope and that an off the shelf corrector would not work.
The owner of the scope uses it visually as well as for imaging with a Baader MPCC.
Here's part of an e-mail he recently sent:-
"Got a great view of Jupiter 2 nights ago. Io was approaching and I saw the moon and its shadow transit the planet and following the shadow was the GRS in pink with a ring around it.
Compared to the refractor the 16in was superior. The globe sizes are similar using 5mm Nagler in the refractor and 15mm Superview in the cass."
I also include a pic of M22 taken through it. I don't think coma is the biggest issue.
It may be poorly designed and less than 1/4 wave because of the large central obtsruction but it is definitely usable.
Your 25" should be better still.