I will say this: the $40 rail was easier to install, feel like better quality in my hand, has numbered rails, and cross bolts for extra strength than my $140 yankee hill machine rail.
My yankee hill machine rail required some fitting and filing to install, has fake cross bolts, does not have numbered rails, and provides a rock solid mount.
The gmg rail required no modification to install, has reinforcing crossbolts, has numbered rails, provides a rock solid mount.
The yhm rail is of excellent quality, but i prefer the gmg rail based on features and price
Ive never had a single problem with my yhm rail. I own one. And will never buy another. I have never had a single problem with my gmg rail, i own 4 for different rifles. If i need another, it will be gmg.