A: Thanks for your question! The add-ons are one-time-use signature credits. The system always uses the reusable credits first, so if you have 5 reusable and 5 one-time-use, if you only use 5 in a given month then you keep the 5 one-time-use for another month. The one-time-use credits also do not expire so you can keep them for if you have a month where you exceed the reusable amount.