I got very used to having quad rails from Knights Armament on my duty M4s. While I am not interested in shelling out that much money for rails I was convinced I wanted and needed quad rails for my personal AR to replace the standard handguards. I had no interest in M-Lok. So I started looking at M-Lok. I like the cost, even the big box store sells the length I need for about $35. Bottom rail section for a vertical grip and flashlight would be about $10 more. Which puts it about half the price of even the cheapest metal quad rails I can find. My biggest concerns are comfort, build quality, and how well they can support at most 2 rail sections. Rifle in question is a PTAC 18" upper.