On my 2008 RT, I had the small and not-loud pancake horn. I bought the parts and installed the two BMW OEM horns over a year ago. Once I figured out where everything was located, installation was not extremely complex, but did require two focused people. I didn't remove the headlight/nacelle pieces.
I think I have used the horns about four times in 16,000 miles...twice with women drivers who had cellphones to their left ears as they decided to move left into my lane on Interstates, once with a person wearing headphones who stepped off a curb directly into my path, and once with a couple of deer considering crossing the Blue Ridge Parkway in North Carolina (they didn't). That said, I frequently have my left thumb on the horn switch in traffic situations. I do try to look down the road a bit, and attempt to foresee problems before they become difficult, so I don't press that button very often.