The Manifold reverse osmosis system from Watts or Watts Premier is a system that has been around for many years and has proven very efficient.  The filter packs for the 4 Stage and 5 Stage are identical with the exception that the 5 Stage system uses an additional external polishing filter.  A few of the brands that are identical are the following: Flowmatic, Watts, Watts Premier and others.  If you have questions, please e-mail us at info@uswatersystems.com or call one of our water experts at 800-608-USWATER.