Im coming to this mouse after using an MX Revolution for 4 years. This mouse has more buttons and fancy software but it pales in comparison.-Its not recognized in Setpoint so you must use the Gaming software to assign your buttons.-The Gaming software will not save the settings for more than a day, so you have to keep resetting the button layout.-Battery life is a joke. You might as well leave it plugged in.If this mouse was free I would still be angry. Please don't waste your money.Update (Oct.29,2013)For whatever reason this mouse has gotten better at keeping profiles. I think it helps to pull the battery every once in a while. Its a good mouse if it saves your profile.I have added a star. But still very frustrating when it drops your profile while you're in the middle of something. 

Question: Does have a extra button?
Answer: This mouse has more buttons