This rocks. The VF appears to be much larger, a perfect size now. Everything is easier - manual focusing, checking exposure values. Take it off and you wonder how you were able to use such a tiny finder! (answer - quite easily actually but still..)
Only downside is if you wear glasses. You will not be able to see the corners unless you move your eye around.
I bought the magnifier and haven't used it except to test it... but to comment about the seeing the corners with glasses, tend to do this now even without it. =/