yes, you can add any brand gfo/carbon/biopellets/etc you want into the reactor. just do not use any kind of mesh or filter socks inside, and follow the directions for the individual media you are running. Do not combine different media into one reactor.
i use TLF Phosban media...has worked great and lasted a long time. No experience with the BRS gfo, but I assume it's like the rest of their products and a great bang for the buck!