Cheap imported canisters and fittings that are not ANSI/NSF approved or UPC rated, low quality, high micron short lived, sediment and carbon block filters about as effective as a screen door, often no name clone membranes of questionable quality, outdated and dry DI resin bobbing around in a little dinky horizontal hollow tube or two, imported by the boat load and sold to unsuspecting users who think they are getting the best thing since sliced bread. You tell me whats wrong with them?
Compare one to a Spectrapure for $129. Built in the same AZ city for over 28 years using nothing but the best ANSI/NSF tested and approved canisters and fittings so they will not crack or burst under pressure and the plastic will not get brittle, absolute rated low micron sediment filter, 1 micron 12,000 gallon carbon block, specially treated to improve its GPD and rejection , high rejection rate 90 GPD RO membrane, 20 oz of freshly blended DI resin, an inline pressure gauge, a capillary tube flow restrictor you yourself can adjust to fit your exact water conditions and more.