I've been very happy with FriendSheep dryer balls - have a few sets for me, and have given sets to younger couples as a gift with a bottle of the scented oil, makes a great gift.
I hope they'll last many years and assume they will - after several months' use they look just like when they arrived.
Fun to be able to use whatever scent you'd like that day :]
Bonus: they do a great job of fluffing comforters & coats - I no longer need to insert a tennis ball in the dryer for those items.
Only slight drawback is that they don't eliminate static cling like plastic/chemical-laden dryer sheets, but I can deal with the minor inconvenience.
Great item, thank you!