My original question was posted in january 2003, thank you for your answers :-). I've bought a JMC 810 at the beginning of february 2003, one year and two months ago, and I'm very happy with it after several hundred of films. Quick and easy to fold and unfold (I do that very often to look on the ground glass), very light with enough rigidity (it's not a Sinar P !), very well crafted, with a modern and discret look pleasant for my taste. Well designed for landscape use, good front movements, especially rise and fall (which can be inverted), and a bit of shift (I sometimes use it) and swing. I never missed the lack of rear movements. Just a complaint about the tightening of the back : the camera is not very rigid, the back doesn't move, it's rather springy, but if one does not tighten it carefully, it can move a bit when one introduces the film holder. Good ground glass and Fresnel, clear but not very contrasty, the camera is sold without GG protector. Good flexible bellows. For overseas buyers, it would be a good idea to provide with the camear some US hex keys (hard to find here in Europe) and some replacement washers and bolts. The three rear knobs are very close to each other, but no problem to use them. Despite the sometimes chaotic sliding of the rails aluminium against aluminium (easy to set), the camera is very fluid to use.
I use it with a heavy 155 (a Sinaron W - a Grandagon in fact - weighing 1.5 kg), and light 240, 305, 450 and 600. No problem with the 155, rigidity is OK, I only miss perhaps 1 cm of rise with the standard bellows. No rigidity problem nor vibrations with the long extension of the 600, all the pictures are sharp. I am waiting now for a 5x7" reducing back. I wrote to Keith canham to know the release date for this back, but I had no answer.