Your photograph has interesting dynamics but it definitely comes off as underexposed to me and what is that v notch on the left side in the black border by his shoulder. That'll never work. Spoils the composition. I have used my Rollei in weddings with a Vivitar thyristor flash and just set the film speed on the flash a stop or two too fast and then figure the exposure on the camera as if not using a flash.
Too bad it won't mount on the other side, you tend to do less winding than you do focusing. BTW, I just bought a couple of original flash units that I'm going to try and convert to electronic. Vintage look, modern operation. One has a big dent in it, so that will be the prototype, the oether is supposed to be in great shape.
The handle is close enough to be able to hold it and focus almost as normal, so its pretty convenient as it is. You can also mount the flash on the other side and you can actually do the half turn on the winder that is needed to wind the film and cock the shutter. The only thing is that you have to wind the new film and place the handle on the ready position before you secure the bracket in place.
To tell your the truth, its far easier to have the handle on the left side, which does not interfere with your focusing at all, hold the camera by your left hand, while you wind and release the shutter by your right. Aperture and shutter can be adjusted as normal. That is of course if you are right handed. I am sure left handed people can reverse this with ease.