Welcome to AA!
That looks like a DIY
filtration system. These were very popular some years ago (some folks still swear by them...less costly than the filters available). The good thing about this one is it does have the 3 stages of filtration.
If you are familiar with the setup, by all means use it. If not, there is plenty of DIY
information available to set it up again (hoses and clamps, etc.).
If you decide you don't want it...finding a buyer may not be difficult. AA has a classifieds section to place an add.