From the same site, different page:
"Although the pump controls the unit completely and does not need a shut-off valve to shut down the unit, some prefer performance with a shutoff valve. There are special "90% shutoff valves" on the market sold to work with the permeate pump. It shuts the unit down when tank pressure reaches 90% of the inlet pressure. We haven't yet found a "90% shutoff valve" that we recommend. You can run the unit with any standard shutoff valve and it will improve the unit's efficiency and the quality of the product water, but you will still have only about 60% of your input pressure in the storage tank."
Ohhhh boyyyyy. So "By far, the best installation involves taking your RO unit’s auto shutoff device completely out of the system and allowing the permeate pump to shut the unit off when the tank is full. That way, you’ll get full line pressure into the tank." Yet it's more efficient to have a shutoff valve, according to the above quote. So how does that make NOT having one "by far, the best installation"? Ughh.