The rails seem to be of good quality, however, there were a couple of issues.One of the 1200mm rails was severely bent (about 1mm at the center). The rail consists of a steel rod and an aluminium base screwed together. I have disassembled the rail, and to my surprise it was the aluminium base which was bent, the rod was perfectly straight. I have straightened out the base by carefully flexing it in the other direction. Mounted the rod back, and fastened the screws by tightening them carefully with the same torque. Now it's perfect.Some buyers have also reported here that some of the bearings do not glide smoothly. Please note that there are two screws on the side that can be adjusted for a smooth glide.
KLaus Wittmann 
