You can see at my gallery or website that I have more than a few shots on the street with a handheld Hasselblad. I even have a couple of threads about it if you take the time to look for them (I gave up).
-Its heavy. Even the basic WLF+80 lens+body+back weights a bit. Winders and dioptres are no-no, a Polaroid back would be trouble and it better hangs from your neck. Other lenses are larger and much heavier than the 80. But I have wielded a 180 telephoto, with the bellows Pro Shade extended at the face of the riot police during a demonstration. Its not much heavier from my Nikon F either.
-The backs are time consuming for loading and the 120 film has too few frames, so you would need to often change film, which is slow and uncomfortable: you need some shade, better rest somewhere and take your time to load it correctly. Plus forgetting the slide in can become a tiresome routine!
- Taking out the film, discarding the foil or sticker (properly), licking the paper backing together (why don't all manufacturers use stickers like some do?) and making sure its not exposed to hard light before it goes in your pocket/pack, can be a nuisance. Let alone when the damned "stamp glue" paper doesn't stick and needs tape or something to hold it together. But unravelling only has happened to me maybe twice.
- The shutter is loud. But you can get by masked by regular street noise.
- The focus is very, very, very, excruciating slow, so you better be able to judge focus by eyeballing the distance!
- You need a lightmeter, but you can take general readings a couple times and fine tune exposure by eye when you move to a differently lighted area.
- It doesn't have the most comfortable and secure grip, but only if I run with it chased by some mean spirited people, I would be concerned.
- It cannot go unnoticed: the retro style of a large unfamiliar design attracts the eyes of people and most often you don't want that. But it can draw interest and sympathy.
hmmm... what else...
Oh, yes, amazing quality of photographs and usually worth the trouble!