Debit cards are very useful to fund casino accounts. They can be directly registered with the casino, making additional registrations with foreign payment providers needless. Debit card deposits will be deducted from players bank accounts and are instantly available (please keep in mind, that the deposit can only be processed, if the debit card PIN has been provided). However many players refrain from giving out their personal debit card details to online casinos.
In general, debit card withdrawals are possible in most countries, while MasterCard branded debit cards might restrict cash-outs.
