I like my BFS 4-stage 75 GPD. At 70 PSI I can make about 100 GPD I prefer the BFS DI resin over BRS, seems to last longer for me. BRS resin seemed to change colors the first day I used it. You don't have to start with one, but I'd highly recommend getting a dual inline TDS meter so you can measure after RO and again after DI, so you know what you are getting and when to change your filters. BFS comes with a handheld meter so I use that to check my tap or anything else I may need to, like an ATO reservoir.