Matt, I have the big heavy eye level finder but the one I use all the time is the WLF, they come in two models, a one touch, which I have, and a double action to close. The one touch or single action is extremely handy because it closes fast. When I started on a Mamiya 645 over thirty years ago all I had was a WLF, I guess I got used to it and now prefer it even though I have a new Prism finder with meter for the 645. With the RB I'll be using the WLF and my Pocket Spot. Good luck luck with the system.
Curt