Hi, I only can speak of the Kippon 645 with focal reducer. It states in their website that it corrects some of the issues with adapted 645 lenses.
I do not know if this is true or not but I can say that I am happy with the results and that I would recomend it.
I attached some samples with me pushing the lenses to wide open which in theory should make for the worst performance
problems with focus are human error probably
https://imgur.com/a/d1SXoyf