My Bronica ETR, SQ and GS-1 cameras all have Speed Grips which work well and allow me to hold the cameras with my right hand. I also have an SQ-AM. The Mamiyas are another story. I don't really like the left hand grips for the M645/1000S/J or RB cameras. For the M645s I got the motor winder just so I could have a right hand grip. The problem? With an insert, a prism finder, a lens, the motor winder and 6 AA batteries, you have a very heavy set-up. I carried a 1000S with all of these things and a bag with three more lenses around Montreal for a day several summers ago. I have a motor for my RZ67 but that's more suited for use on a tripod. An RB67 with a WL finder, a back and a 90 is not that heavy. I prefer to hold it without the left hand grip.
A few days ago I shot a roll of 120 Portra 400 with an SQ-A with a WL finder and a 50/3.5 S lens. I don't mind the laterally reversed image. My Yashica Mat 124G from High School had the same view. How did I meter? I used a Minolta X700 with a 50/2 lens. Generally I wouldn't use the Speed Grip with a WL finder. I have a number of prism finders and a metered chimney finder for my SQ-As but the WL finder is light and doesn't take up much space when it's folded.
I don't mind the grip for my Koni-Omegas. The problem with that camera is the loud film advance. It can sound like cocking a gun.