I have had the 100mm previously. I had mixed feelings about it. The thing that comes to mind is to use it for portraits, but I found it was hard to nail the focus in most cases, especially in the "not recommended" close-up zone, which would be a let-down for portraits. Also the framing would become very approximative, and the 135mm framing would be even more difficult.
You need to check the frame lines on your body. Only early bodies (serial number starting with 0) are supposed to have the 135mm frame lines (unless the body was modified after production).