Juice Defender is a must on any phone IMO. It will turn off your data when the screen is off. It works great.

As for an App killer the Epic Touch has one build-in. Do now worry about using one.

 

I see no reason for bieng with or against this app. It's free, try it and if you see an improvement it's a good thing . if not uninstall it.
But to really answer under the topic, frankly I doubt that this kind of software do miracles, everything it does you can do it manually, and even maybe you do already. Otherwise I do not like "When CPU scaling phone is idle" I do not like that one just breaking through my CPU frequency only to earn 1 hour or 2.

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