A Bronica ETR series with a 50mm lens and a simple prism is a nice street shooter. Waist level if you want to be tied to horizontal format and the reversal works for you, AE prism if you want to not think about metering. No need to add a grip, I found.
I've found with both a Bronica and more so a TLR, looking down into a waist level finder makes you disappear from people's radar on the street all in all.
I used a Fuji 645 for a few days.Very nice, very quick, great lens. That kind of view finder is a very different way of framing than an SLR's (or TlR's) ground glass. I just started using a Fuji GW690 on the street and it's a kick.