Is it? If it's just on your key, you get out, park, shove the dongle into the parking meter a couple times, and walk off. Every few days you stop by one of the various shops that could reload it, shove the key in, give the clerk some more money, then not have to think about a pocket full of change.

Literally all the same steps as quarters, except you can’t use it to buy anything else, and need to refill it only at a special place - instead of anywhere that handles cash and can make change.