ANY app that claims to clean unused background apps out of RAM is saying that the developer doesn't understand how Android works - and I wouldn't allow an app written by someone like that on my phone. (The developer of a piece of software knows how it's supposed to work better than anyone else can. Read
Multitasking the Android Way - by a Google software engineer - and you'll see why cleaning apps out of RAM is the opposite of what's supposed to be done.)
You can clear the cache in seconds (Settings/General/Storage/Cache).
Greenify works. It keeps apps from running unless you run them. (So you don't want to Greenify Phone, email, texting, etc.) Of course any app uses RAM and battery, but if it saves more battery (and RAM, in some cases) than it uses, it's a good thing. (Android handles RAM, so unless you have to have a few large apps running at the same time, or you have a phone with a small amount of RAM, RAM isn't something to worry about. Battery consumption is, and you don't save battery by "removing" apps from RAM - when they're not running, which is what some of these apps do.)