Has anyone used the Mamiya 7 external viewfinder for the 150 and 200mm lens? What does it do?

Has anyone in this community used the Mamiya 7 external viewfinder for the 150 and 200mm lens?
It is not a piece of equipment which is easy to come by with to just "try it out", so was wondering if someone can give me some insight.
Considering the rangefinder viewer of the camera does not bring you "closer" to the subject when you change lens but just adds tighter cropping lines the higher you go in the focal length (65->80>150),
I was wondering if the external viewfinder instead brings you closer to the subject.
Many thanks for the advice!

My understanding is the viewfinder does magnify more than the built in viewfinder and has frame lines for both 210mm and 150mm lenses. It does not help with focusing and the focus distance must be set on the finder to account for parallax. I have thought about getting a 210mm lens mostly so I could get the finder for more accurate framing on the 150mm. But like you I would like to test it out first. If you do find one to look through please report back how much difference it makes.

I have the Mamiya viewfinder for the 150. The purpose is to give better assistance in framing and composing. The camera does not read any info as it sits in a cold hotshot. Focusing is done through the camera's viewfinder. It is essentially a three step process: pick your subject through the camera's VF, then bring the attached VF to eye level, frame and compose, then back to the body's VF for focusing, and click.