rodi filters

Okay, so I’m not keeping seahorses lol But I haven’t seen much online about folks using the Aqua FX Seahorse 4-inline RO/DI and I wanted to see if anyone on here has had experience with one. It’s my first time using a RO/DI and chloramine filters and the instructions provided aren’t super clear...

Right now I am running 4 stage value 75GPD system, I want to add 2 more stages and run the Pro series cation, anion, and mixed bed from BRS. Is it that simple to add the 2 extra canisters? Will 2 stages of DI work? Im looking to remove silicates.

So I was gonna buy a 10" standard RODI Unit but it's like $300 brand new (CAD), but I seen on my local classifieds that someone has a 4 stage (or I think it's actually a 5 stage) for under $100 (CAD) but unsure of the brand (seems like it has no name), but the person said it's practically new...