I recently acquired a Pentax 67 that came with the 67 TTL Prism. I'd rather meter handheld with all my film, so I never loved the extra "bar" for the shutter coupling, plus I found it to be rather dim and hard to view with glasses (that got scratched from the metal eyepiece. Instead of spending the cash to upgrade to a P67II or buying a Maxwell focus screen, I thought I'd try a P67II prism on my P67.
The results have been pleasant, it's about half a stop faster, is a bit larger viewfinder and has slightly better eye relief (with a rubber cup). Plus for my vanity, the lack of TTL bar looks much better. A moderate upgrade for $100, that I'm very pleased with. Here's a visual comparison in the prism.