I have the 3 stage chloramine / chlorine only filter. Stage 1 is a sediment filter, stage 2 and 3 are carbon block chlorine filter cartridges. I don't do RO/DI filtering--that's for saltwater tanks.
The filter cartridge I linked to above is not a RO/DI filter, it's a chlorine filter. So, I'd buy 2 of those, and 1 sediment filter for stage 1, as replacement cartridges for the 3 stage housing I already have from Filter Guys. I just need replacement cartridges.
"BRS Universal Carbon Blocks have been specially formulated for industry leading chloramine and chlorine reduction"
If you don't have the filter housing, then just get a 3 stage filter housing and put the right filter cartridges in it to achieve what you want -- for most of us keeping CA/SA cichlids, we just want chlorine and chloramine removal.