I've got the T-Rex case guards and the R Gaza bag guards. The finish on the R Gaza pieces is similar or identical to the T-Rex, and they fit just as well. The mounting hardware is not quite as nice.
The T-Rexes are joined with fairly nice MIG welds. The R Gazas apparently use stick welding, well-done, but thicker and cruder-looking. Also, they don't have the sacrificial, replaceable strip of metal the T-Rexes have.
On the bike, the differences aren't really noticeable, and, besides the metal strip, seem functionally identical.