The Fein Multimaster tool and associated blades are invaluable for those specialized tasks that no other tool really does well, as advertised. I used these blades to custom fit a cabinet for an under-counter fridge where some cuts were necessary that would have been almost impossible with any other tool. Very easy, very tidy.
However, the blades wear out quickly and are very expensive. It is too bad Fein won't make them out of bi-metal, or lower their price point. They are missing a much bigger market out there, in my opinion. Use them when you must, but only when you must.