As I write this I'm on my way back from a week in Xi'an, China, where among other missions I'd thought of trying to pick up a Great Wall camera from the street market. (It's a 6x6 SLR of a very primitive character.) In the end I didn't, but I had an interesting time trying.
Xi'an has a big street-market district around the Great Mosque, but most of it is either food (very good) or tourist bait (mostly cheap souvenirs, but I bought a working gourd flute from a nice old Uighur man whose sole word of English was "This"). I only found a couple of shops with cameras. The first one had a Hongmei folder; I asked the owner how old it was and he looked at me gravely and said "Hundred and twenty years!" so I laughed at him and left. Didn't want it anyway; I have good triplet folders, I don't need a bad one.
Eventually I found a shop that had a couple of Seagull TLRs and Phenix rangefinders on display, and the owner thought he might be able to find me a Great Wall once we determined what it was. (I couldn't remember the Chinese name "Chang Cheng", so I drew a picture of a little box with one lens and he figured it out.) When I came back a couple of days later, in fact he had produced one, and while in the end I didn't buy it because he simply wanted too much (he started at 1100 RMB or about US$165, and seemed very little inclined to bargain---either he was bluffing hard or he really had paid a lot for it himself), I worked it over pretty thoroughly while discussing the matter and thought it might be of interest to report what I found, since there don't seem to be a lot of these cameras in circulation outside China.
The camera was *very* primitive for an SLR---no instant-return mirror, even. To see through the viewfinder you have to energize the shutter by flipping a little switch and turning the shutter-speed dial---then the mirror, which is *part* *of* the shutter, goes down and you can see. (The viewscreen has a terrible rep but didn't seem all that bad to me---not much worse than the original screen on my Rolleicord.)
The shutter is just bizarre; half of it is the shutter, the other half a panel that flips up from the bottom of the camera. As far as I can tell, releasing the shutter raises the mirror to open the shutter, and the expiration of the timer releases the second panel, which closes it. (I don't know how it stays closed during the process of lowering the mirror to energize.) Impressively, the shutter seemed to work fine at all speeds. The only thing wrong with the camera, per se, was that the focus was loose (but working) and the lens had a little bloom of haze that could have been nascent fungus or could just have been a bit of cleanable gunk.
It felt as clunky as any camera I've ever handled, but seemed actually to be pretty structurally sound. The body covering had a strange tacky feeling, nothing that shed goo on my hands but enough to make me wonder what in the hell it could have been made of. It felt like all the joints and fittings were extremely imprecise, a sort of anti-Leica sensation, but everything did in the end seem to move as it should.
I'm disappointed that I couldn't get to a price I could justify; this camera had character and inspired some affection, even though I'm not really an SLR guy. I have an easy time believing that the peculiar shutter would cause some unevenness of exposure as it's reputed to do, but other than that it seemed like a very functional shooter for someone who didn't mind the somewhat complex handling. I'd say, if you find a cheap example, buy it.