"I asked this before and got hammered, but I'll ask it again. What, exactly, is the problem with external view finders? I use them all the time on my Leicas and R-D1. What's the big deal?"
Well, here's a list:
1. An external VF tends to snag clothing. I could carry (say) an R3M with 25/4 Skopar in my pocket, but the 25 VF makes it hard to get the thing out to use.
2. An external VF tends to disrupt your working style. With Lens A on your camera, you frame, focus, set expsoure. Switch lenses on that camera, mount an external VF, and you've got to now check the external VF in addition. With short enough lenses, you can just scale focus and concentrate on the VF; then, working with an external VF becomes pretty nice. That doesn't work nearly as well with a 75mm external VF.
3. With some cameras/VFs, it's too easy to lose that external VF. And on the other hand, I've used a couple of combinations where it was near impossible to get the shoe to release the VF.
4. External VFs slow down the process of switching lenses. It's one more thing you gotta do, and time can be precious, on occasion. Worse, the VF can get separated from the lens, so you gotta hunt for it in your bag. And just maybe, you discover that you brought the lens but left the external VF at home.
5. Some folks have other uses for that shoe, a meter maybe. (Not me, but it's fairly common.)
Now, none of those bits of awkwardness is beyond conquering in some way. In fact, I still use an external VF in some situations. But if I don't have to, I'd rather not.
In my own case, I use mostly 25/35/75 lenses and, very rarely, a 90. An R4M lets me switch quickly between 25 and 35, and M4-P (among others) lets me switch quickly between 35 and 75. Generally, I've got 400BW film in both bodies, so I carry them with 35 and 75 mounted. Once in a while, I decide to shoot some color. Then, I'll use a 25 external VF with the M4-P, or a 75 external VF with the R4M (but not at wide apertures), as need be.
Nothing wrong with external viewfinders that can't be tolerated. But the R4M does away with a lot of need to tolerate some awkwardness with wide angle lenses.
My $0.02US.