My experience with Proporta is that the cases themselves are made of top-flight materials and assembled beautifully. Unfortunately, the case designs themselves are not the most practical.
I had a Proporta Alu-leather case for my old iPAQ 4355. I bought it for the added protection of the aluminum-lined front flap. One night I was holding my oldest son in a parking lot and his leg popped the case out of its quick-release snap. The iPAQ was badly scratched and the plastic housing around the QWERTY keyboard snapped off the device because the sides were completely unprotected. So the aluminum cover was only usefuly in the extremely unlikely event that the device fall perfectly flat onto its front face (of course it was also well protected against a .22 caliber round fired directly at the front cover, which is also highly useful.)