This is a really good idea if you're in a position to be putting any cash savings aside. In a perfect world everyone would have 3 months of expenses in cash savings, obviously that's not always realistic, but if you combine that with an offset or revolving credit then you have the benefit of having that safety net while still saving the interest cost on that money. Our offset mortgage saves us about 100 bucks a week, a good chunk of that is just my provisional tax sitting aside waiting to pay the IRD.