Are these things any good? I like the idea of having the opportunity to shoot different aspect ratios of rollfilm with a technika I'm going to buy. This apparently covers a few all in one back. I want to be able to shoot 6x6 and was thinking of cropping back from the 6x7 rollex back the guy is including with the camera. Any info would be nice. Whether anybody has used one. I like the idea of being able to shoot 6x17 panoramics too as cameras specifically designed for shooting that ratio are rediculous expensive.