Hi Lightbulb
If someone gives you an interest free loan and you use it to pay down an expensive mortgage, then you will save money.
The two most popular cards in Ireland are BoI and AIB Visa. Both charge a 1.5% cash advance fee and then interest at rates up to 20% a year if you don't clear it in time.
So if you borrow €10,000 on your credit card for one month, it will cost you €150.
If you pay the €10,000 off your mortgage and you are paying 4.5% a year APR (currently the highest mortgage rate in Ireland), you will save €37.50 mortgage interest (10,000 @4.5%/12).
So this transaction will cost you over €100 net.
I don't think that an interest-free and charge-free credit card exists in Ireland. But if you can find one and you pay €10,000 off your mortgage, you will save €37.50 interest per month. However, there is always a catch. For example, if you miss a credit card payment date, the charges you face will be a multiple of your savings.
Brendan