I bought a bottle of R-0872 to go with my K2006C kit in order to test specifically for Bromine, having the same thoughts as OP. After I learned that either will test for FC AND bromine, I just left the R-0872 in the kit. Out of curiosity one day I repeated a FAS/DPD test in my pool water using 10 mL samples, one with R-0871 and one with R-0872. It took 19 drops of R-0871 and 15 drops of R-0872 to achieve color change. That led me to believe there is a concentration difference between them. The difference seemed too much to be a margin of error.