Batteries: Most transmitters have batteries that need to be charged, usually the day before you go flying. But if you forget, then no flying. The Spektrum DX6 takes AA batteries. With AA batteries, no charging. You are always ready to fly as long as you have some AA batteries.
Timer: You set the timer to count down so that it beeps before your batteries run down all the way. You hear warning beeps as your time gets shorter. But if the timer keeps running when you are at low or no throttle, you get less flying time even though you are using much less battery life. So with the DX6 you can set the timer to cut off when you go to low or no throttle. That extends your flying time. And every time the throttle goes below the threshold that you set, you get a beep to let you know that you are extending your flight. Two great features.