The exchange rate on these 'free' cards is usual poor - there's no such thing as a free lunch! They will get their charges one way or another! In the eurozone a good method is a pre-loaded debit card such as FairFX, so you can see the rate at which you are buying and use it at ATMs or as a debit card in Eurozone, its backed by Mastercard and Newcastle Building Society. Apply and service online, but keep check of the balance manually because the only way to check the remaining balance is by text for which a charge is made. I don't think you can overdraw on it.