For What it is worth, I have used Rollei, Mamia, Pentax a great deal, The rollei made the best negatives I have ever made, I went then to several Hasselblads and have never gotten the same quality negatives that I did with the Rollei. I still have the Hasselblads and a lots of lenses, but they in no way will compete with negatives I get from the Pentax 6x7. The results I am speaking of here are the results I personally have been able to achieve not here say or maybe. I have the negatives to back up my comments.
My Rollei negs are the sharpest I have ever made, My hasselblad negatives made with several different bodys and lenses(still own three) are very good, but not comparable with the Rollie or Pentax.
I owned several RB67's and liked the way they handled, but never was able to make l'st class negatives with them. The mirror slap in the Pentax
while being hand held during weddings etc. has never been a problem for me. I supposed I have hand held it for years, since I didn't know any better. :-)
My Rolleiflexs three of them packed snugly in their Halliburton case deserted me for someone else off of the carousel at LAX . I have never replaced them.
My comments here are in no way a slap or slam at the products that have not performed for me to my expectations, I simply have related my experience using them for a lot of years makeing negatives with them.
I personally do not like the square format, but often have used it to aid in
telling my picture story. I much prefer a horizontal rectangle, but would not argue/debate one over the other.