I absolutely agree, I actually logged into the forums for the first time to post this very same feedback, but then I saw this thread
I bought this mouse specifically for game keybinds so I must say I was very disappointed when I discovered that RoM did not support additional mouse buttons.
I really hope they implement this soon, I know its probably not on the top of their list when it comes to urgent changes, but I can't imagine it is something that is particularly difficult to implement.