Many many years ago I had a Hasselblad 503CM. I used it for product photography, some portraiture, and a bunch of polacolor transfer work I was doing for editorial illustration.
I never bought a pentaprism for it, instead using the collapsible focusing hood that it came with. Without a pentaprism, everything in the finder was of course flipped and flopped. Upside-down and back-to-front. And this meant you really had to think about your composition to make sure you were going to get what you hoped for.
Now I shoot much less frequently, and I use a 40D, which has ‘Liveview’ on the LCD panel on the back. And I wish there were an easy way to have that image rendered flipped and flopped, so I’d spend more time thinking about shots I take.