Tired it once, never bothered again.
Rinsing agents for automatic dishwashers may contain some acid substances to counter the alkaline of detergents. Rinse agents also contain wetting agents, surfactants and other chemicals to make water "sheet", off dishes leaving them without streaks and splotches. Keeping final rinse water slippery also ensures any food particles still around won't end up clinging to dishes, and even worse being baked on during heated drying.
Have been using Ecover's rinse agent for awhile now and am quite pleased with the results. It does contain citric acid, and other natural agents, but dishes dry spotless, even on "energy saver".
L.