Not sure how much they charge if you stick a US debit card in there (I assume it’s a lot), but if you are using Local Bank A and go to Local Bank B for cash withdrawal, you pay a 15NT transaction fee. This is a flat fee across all banks. Meaning, if you are using Local Bank A, you pay 15NT transaction fee for withdrawing cash from Local Bank B-Z.
If you’re wire transferring (which is a popular way to transfer money for buying things online or transferring funds with friends), if you friend is using Bank B, but you use Bank A, you can go to Bank B’s ATM to transfer the funds and do not incur any transaction fees. However, if you are transferring from your own bank to another bank, you incur the transaction fee (which I think is also 15NT).