It gets better. It is neither windage nor elevation adjustable, nor is the size of the reticle adjustable.
So if you shoot a gun who's POI is any higher than 50/50, you're SOL. And that all assumes your rib is in perfect alignment with the bore of your gun.
This thing would be all but useless for someone shooting a gun with a 9" high POI and a full choke @ 16yd.
Burris Speedbead/Fastfire, Leopold Deltapoint, or Eotech would all be vastly superior, and a rib style mount would not be that difficult to fabricate (or piece together from existing components).