It all comes down to personal preference and personal usage of the phone. Some have good experiences with atk's and some have bad. It's just like any other system app that people have positive and negative experiences with.
The bottom line is; just test a few atk's out and see the results, that will tell you if they save battery. I personally don't see a point in using an atk on an android phone, but that's just me.
On a side note, I flashed the latest leaked rom which has a task killer pre-installed (which I removed after flashing) and I get wonderful battery life and I have been abusing my phone for the past 3 days since I flashed (i.e. gps, fb, wifi, browser, texting, phone usage, live wallpaper, etc.). So if you're that hooked on using a task manager, flash to the new leaked rom.
