The Root Explorer devs have a 24 hour refund policy despite Google's 2 hour policy. All one needs to do is e-mail the devs within that 24 hour period to ask for a refund.
As the name would suggest root file access and editing is something Root File Explorer excels at. It was one of the first to have this function and is still one of the best.
AdBlock+ has an automatic whitelist when installed that allows certain advertisers through the blocking mechanism. The fact that these advertisers pay for this privilege makes this particular scenario rife with conflict of interest.
The Greenify (Donation Package) has a few extra experimental features that the free version does not offer. They require ROOT and the Xposed module to be installed. Using these features can help with the compatibility of the rest of the Greenify app, which is a big plus.
Greenify's mane function is to hibernate any installed apps. This allows users to to quell overly active apps that are draining their battery without having to delete them. This can be done with or without ROOT.
When using Greenify without ROOT access to hibernate apps, it has to be done manually each time. There is a widget and shortcut that users can set to their home screen to make this action a bit easier though.
Xposed can radically modify the behavior and look of the system and apps without having to modify any APKs. This means that Xposed modules can work with different versions of the same ROM or even different ROMs altogether.