Outdoor water filter is filter for those sand or more big molecule. Outdoor water filter also can protect your indoor water filter for it to last longer for the cartridge.

Outdoor is a general filter for whole house, while indoor is just drinking water (much cleaner than outdoor), hence it is recommended to get both

For outdoor, mainly there are two types
1) Membrane
2) Sand

there is other type like Diamond using cloth also but common will be membrane and sand. Each type has their own pros and cos,so it depends on what u really need as an outdoor water filter

Best Water quality and Design = Membrane

Cost effective, low maintenance cost better flow rate = sand
For indoor, if u need hot,cold and warm, then u need to get a water dispenser