Had I known about the Promag copy I might have given it a try. . .the thing about the Arms 18 mount that I was worried about is that my Norinco m14 might be a "bit out of spec" and the 3 points of contact where the mount fits the gun might be compromised. I also read some reviews/issues with ejection of brass--and the price was prohibitive--I mean the mount is $300, the gun was $500 (?!).
My further 2cents for what it's worth--removing the back sights provides a large/stable area for mounting and this seems like a more modern scope mount design with better consideration for the shortcomings of the m14 platform (like the fact that the mounting points on the m14 aren't that good to begin with). That being said, Arms 18 seems to have been around for years so it must be good, and one would assume that any copies of it are built to the same tolerances (again, that's an assumption, and ymmv (your mileage may vary). I have no experience with either. Good luck.