Used them in the dryer and might've gone a little overboard with the essential oils, but at least the entire house now smells citrusy and divine, haha.
Definitely way better than the plastic single-use dryer sheets because you can customise the scent with your favourite essential oils. However, maybe just stick to a few drops of essential oil per ball (and remember to do this hours ahead of time (or run them in the dryer, by themselves, for a few mins) so the oil has a chance to soak into the ball instead of staining your clothes).