I have the pentair prf RO. With a booster pump it is bringing tds down from 175 to 007. If your tap pressure is under 50 you will need a booster pump in the winter as its very slow without it.
This onehttp://www.gardinerpolesystems.co.uk/acatalog/Booster_Pump_Reverse_Osmosis_PRF-RO_Systems.html