Wonder if there is an iPhone or android app that could easily display the amount of camera shake? place the phone inside the WLF and play around until you find a personal solution. Would also be nice to do this with a bubble level so you know its both steady and straight.
When I got my RZ67II a few years ago, it took a while before I got used to the bulk. The L grip definitely helps. As you've discovered, this camera produces some stellar instant shots with the Pola back. I probably capture 50% of my pictures through that alone.