A super wide needs to be used carefully, or the wide angle distortion will be bothersome to look at.
I don't know what the 35mm camera equivalent lens would be.
I used a 24mm lens on a 35mm camera, and I always had to be careful not to tilt the camera. And I would not use this lens unless I had to. It was too wide for normal use.
Is it possible to rent that lens rather than buying it? Then you can see if you really want to buy it.
The Mamiya 43mm is almost a perfect lens, if you have a straight line going across your image, that line is perfectly straight all the way through, the 35mm equivalent is roughly 21mm. It's an amazing lens, the most sharp 120 lens ever made, there are posts out there I've read on how to LESSEN the sharpness because it's so sharp. It's beautiful, and I love mine, many of my grand canyon shots are used with it, and that one of the cross on the hill (it's only square for reasons of some headlight fog I got from a passing car on a 10 minute exposure).
My only warning is make sure to buy one WITH THE VIEWFINDER ... I did not, it's such a pain, and they are SO expensive, it's just dumb, I'm desperate for a viewfinder for mine.
EDIT: I love all 3 lenses I have, the 43mm, 65mm, and 150mm, but if you want an "all purpose" lens, go with the 65mm, I tend to use that one a lot.