I have ATK installed on my Evo. I do NOT have it set to automatically kill apps. It's a handy way to manually see what apps have been restarted. But using it to kill badly behaved apps is like using a band-aid to treat a stroke. Or maybe it's more like using open heart surgery to fix indigestion. If you've got a bad app, remove it. In the case of the Facebook app, uninstalling the update fixed the problem more thoroughly than would ATK.
A better approach to saving battery is to look at what apps are using cpu and battery (System Panel and SpareParts are free apps that will help), and then check the settings on those apps. For example, set Gtalk to not automatically log in. Set apps that do background syncing, but that you don't use, to not sync automtaically (e.g., stocks, facebook, news).
There's are multiple threads here and on other Android forums with more detailed suggestions on battery life.