You have a problem with Reading Comprehension, I never said it would fail...I said its something to consider. If I had a $500 TV, I wouldn't give a crap if it fell. If it was a $2500 TV, I'd probably skip the $30 mount and buy the $150 mount instead if only for peace of mind.
Mounts are all made of metal, but the quality of the metal, particularly of the parts that hinge the brackets together, are where you see cost cutting. Stamped versus forged steel for example...the quality of welds.....all of that makes a difference.
You can tell yourself that the $30 mount is the same as the $150 mount, but in many cases thats simply not true. Having said all that, I dont know about the Monoprice mounts.......its just something to consider if you can't afford to replace your TV if it fails.