I use task panel. After using ATK for a week, I had no difference in my battery life and I kept having to close out the apps. Unlike with task panel. The apps stay closed and you can keep which ones to keep running and which apps to automatically "kill."
And my battery lasts longer with it. Lastnight it had 80% when I took it off charge at 11:30, and this morning around 11:30 is when it needed to be charged again. So, 12 hours isn't bad at all for a smartphone.