It's the only mount I use as it is the lowest option and allows for not only keeping the iron sight, it affords full use of it when optic is removed. I swap between my nightforce and my eotech depending on my mood and task at hand.
YES an improperly set up rig can give a guy a headache when brass catches. ALL "above the breech" mounts will do this, some worse than others. The arms 18 has a long and reputable track record in both military and civillian use. Some research proves this.
Is it "the best" , nope, there is no "best" , not in a broad sense anyways. But depending on what your needs are, it may or may not be the "best" mount for you.
I have a troy chassis, which offers a mounting height like the casm mounts do. I like this rig for my long range, prone position shooting, but for offhand and bench, the sight plane is just way to high for me.
Anyhow, Arms being out of stock of their signature scope mount should be an indicator of just how popular these mounts are, stateside anyways.