The way I understand this is as follows :
Xapo have a internal ledger system, keeping track of internal transfers between Xapo accounts and none of this is reflected on the Bitcoin Blockchain. So no miners fees are payable to the miners, because these transactions are off-chain. < So doing transactions between Xapo accounts should be free >
If the faucet owner has a Xapo account and you have a Xapo account, these micro <dust> transactions are virtually free. You will only pay miners fees, when you push the balance of you transactions to a Bitcoin address that are on the Blockchain. < This is why they have a withdraw option, which takes the balance from their ledger to a external on-chain Bitcoin address >
So yes, you made the best decision to use Xapo for micro transactions < also called Dust > ^smile^
https://support.xapo.com/is-there-a-fee-to-transfer-between-different-currencies-within-xapo/view=faqMake sure that you adhere to their rules,
https://xapo.com/terms/
