I'm with Roger Cole -- I've used his technique for years (decades!) on TLRs. Works very well for me.
hahahaha depends on what I am shooting. When my RB is on a tripod using a very low angle I use my WLF (chimney).
If I am hand holding I use my prism.
I use a Rollei with WLF, and used a Hasselblad a couple of years ago. Even now the left - right thing catches me out, but generally, you just become accustomed to it. If I could have a prism with no extra size, then I would, but generally the WLF works just great.
Meanwhile, I came to MF with the Pentax 645N system and loved it. Then tried a Rolleiflex and it quickly took over. Yes, I had to get used to the mirror image, but ultimately find the mirror image an advantage, and the WLF a superb plus. Especially if you wear glasses, as I do: I can keep them on with my Rolleiflexes, not with my Pentax.
I loved it so much that I also acquired a Rolleiflex 6008i, which has a WLF, but with meter and interchangeable lenses. It is heavy, though, but handles quite well. It is not sharper than the Xenotar or Planar 2.8 80mm lenses on the TLR, which are indeeed wonderfully silent. I'm going to offload one TLR only because I need the dosh, and I hope to add to my 6008i, and still have a TLR, but otherwise the TLR rules. (I still use my Pentax 645N with 35mm, 135mm, and 150mm lenses. The Pentax also is ergonomically brilliant, has a built-in diopter, and a future upgrade path to the 645D... But the WLF is still my first choice.)
I own a 45º and a 90º prism finder for my Bronica SQ-A but have to admit I almost never use either; I suppose using the WLF also keeps me consistent with my Yashica 124G. The SQ-A WLF is light weight and folds to compact the package. Of course, I don't shoot auto racing or hockey games! :whistling:
I nearly always use a 90º prism on my Rolleiflex. Not only does it give you options to how you hold the camera.. taking lens down or taking lens to the side or taking lens up, and besides orienting the image correctly, it also makes the image much easier to see. You don't have to compete with ambient light and reflections on the surface of the screen as well as you don't have to be taking your reading glasses off and back on. I go the other way from most people on the balance issue. I find it much easier to hold the camera steady with the prism on. After focusing and when ready to push the shutter I cup the top of the prism in my left hand while holding the camera in my right hand. It is very solid.
I have a 90 degree prism and WLF viewfinder for my hasselblad 501c. I never use the prism. First of all the camera is lighter and more compact. Also like others have mentioned, with the WLF it helps my composition. It's only psychological, but it does make a difference to me. When I look down on it, to me it looks like I'm watching a photo and I'm much more likely to reject and correct photos that I would normally take with a prism.
As for the mirrored image and panning etc, I find it quite easy. I just hold the centre of the camera in my left hand, while moving the back of the camera in the direction the object is traveling (or is) in the viewfinder. The lens will follow the correct direction. But it sometimes can become bit difficult on diagonals. If I get all confused, I look up the scene again and back at the viewfinder. It will become second nature after few days.
Also my Acute-Matte screen is very bright even on the brightest and sunniest days in Australia. So the stray light was never an issue.
One handy use of waist level finders is over your head to shoot over a crowd or other obstructions.
When you can pan a moving subject while looking up at your upside down camera, you have passed.;)