I'm a native English speaker in the US, and I've seen and heard this expression in news media in the past, especially in the political context - however, it seems to have become rather hackneyed and is not used so much today. However, I personally have never used it in speech or writing in my entire life.
...and sorry, middle-of-the-box was a typo -- perhaps because my next question (which I have noted down in my diary but haven't posted yet) was about the use of "out-of-the-box". Silly how the subconscience works.