One button? What class are you playing? If you're only using one button to dps on your MERC then you fail. Between popping my trinkets, TM, HS, Rail Shot, Unload, Power Surge, Instant Fusion while watching for Barrage Procs I'd say your one button BS is just that..BS. Also with my cast time on TM at 1.3 secs I'm also able to get in free Rapid Shots.