Not him but I have been using a couple of Mercuries since the first round of shipments from KS, and just ordered a new 5x7 camera.
IMO the best "use case" for this camera is as a fixed-lens ultrawide. My preferred setups are a 38mm lens on 6x9, a 47mm lens on 4x5, and my newest camera will be rocking a 72mm lens on 5x7. These are all extreme wide angles.
I shoot landscapes though. You can shoot handheld street images with hyperfocal zone focusing if you want, and set it up for that.
My only complaint is a bit of trouble with flare in some situations with the sun out of frame using a lens with excess coverage - the plastic body exacerbates it. But that's a rare thing. Use a hood and it's fine.
Some photos:
Landscape 1
Landscape 2