RLR is an old school laundry treatment that has remained unchanged for many years for a very good reason - it works.
If your diapers aren't smelling clean after washing or aren't absorbing like they should, they might have a buildup of either minerals or detergent. RLR can help with both. Just add it to your hot wash cycle along with your normal detergent (one package for top loaders, a bit less for front loaders). Do a few extra hot rinses after this until you don't see any more bubbles to make sure all the buildup has washed out.