Flow restrictors come in several different types of styles. There is the tube capillary flow restrictor that is actually inserted into the tube and the inline flow restrictor that is not only easy to install but easiest to locate as well. Both styles work equally well and there is no really difference in performance. Flow restrictors are required for reverse osmosis systems in order to produce the proper rejection rates of a ro membrane. Without proper rejection, you may be eithe wasting too much water or not enough and cause TDS creep.