[ohthanks]

They don't boost the feed pressure, just isolate the output permeate line from the back pressure of the storage tank. Instead of the membrane output pushing against the increasing pressure of tank as it fills (decreasing output) it produces into a void in pump body which the pump periodically pushes into the tank from spring mechanism wound by the output waste water.

They work pretty well to reduce waste but do add complexity to what is already a somewhat complicated device under the sink. They will also create bad TDS creep if used without an auto-shutoff valve installed in the RO.