I put a Bad Boy from Harbor Freight on my 650 as one of the first things I did. I couldn't have a horn you couldn't hear over the exhaust. The new horn is scary loud.
I originally mounted it where the stock horn was, but the fender rubbed it on big bumps so I made a mount and put it on the right side next too and in front of the breather cover. Looks good there as well.
I say the same about hooking the horn up thru a relay as you will burn up your original horn button if you don't. Do not hook the horn directly too the button, it may work for a little bit, but will burn the button up quickly.