I Have finally saved enough and bought a set of Genuine HIWIN mgn12H 400mm rails + carriages from Blurolls Lu (Aliexpress Store).
Although my cheap Chinese rails are pretty good these Hiwin rails are way better. Only one word can describe them - Perfection !!! It was well-packed, the rails were very clean. The motion as expected is very smooth yet rigid! Don't expect it to just fall when tilted.. it won't! If it's too smooth then you are in trouble, you will have too much free movements while twisting the carriage. At the end of the video, I tried to twist it and its so rigid! Great quality and worth every single penny. I Bought them from HERE Please mind that i paid for the rails set like everyone else. also, no one paid me to write it or something like that.