The linear bearing and Delrin Wheel Gantry commonly used at most of the low-mid 3d printers as a cheaper solution for linear motion. Its cheaper replacement for the expensive mgn rails BUT the price is at the expense of accuracy and reliability. Well, linear guided rails (mgn rails) are much more rigid, extremely precise and smooth then linear bearing or Delrin. The linear rails let you print with higher speed - shorting print time without compromising print quality. The fact rails are fixed to frame prevents unwanted motion related to bent threaded rods or other axis's motion. There seems to be a good reason why they are mostly used with high-end 3d printers.
So, I found cheap Chinese mgn rails at Aliexpress and thought to myself why not?