Fluidized bed filters questions from a noob

A friend gave me 2 "Red Sea Merlin Plus 120 Fluidized Bed Filters". I'm new to this type of filter (have only really used a sump, bio balls, protein skimmer as my filtration for my FOWLR tank) and from what I gather it helps keep phosphate & nitrate levels down but I don't know how effective they are. I have a few questions.

1) What's the benefit of this filter to my system that already uses the above filtration? Is this replacement for other filters or a supplemental filter? Worth using?

2) How does this compare to a "2 little fishes phosban reactor" and of the two which would you choose? (I could sell these and buy the 2 little fishes model for about $35)

3) What type of media do i have to buy for these filters?

Thanks for your help!


Product Info Link:
Red Sea Merlin Plus 60 Fluidized Bed Sand Filter


Here is the manual from the "Merlin Plus 120":