I agree that this battery is expensive. I debated for some time the merits of a cheaper copy battery and the much more expensive genuine Canon product and opted for the latter.
I have found the Canon battery to last an absolute age but wanted a backup. I paid a lot of money for my 450D and decided that if I end up leaving the battery in the camera for a long time I just don't want to take a risk of it leaking. Now, it is true that no one reviewing the copy batteries has had any issues but I decided on balance to go with the Canon. it is a new boxed battery, looks exactly like the one in the camera and also lasts an age. It does what it says on the tin. Why take a chance when you have commited so much on the camera, lenses, flash etc.?