Those that tested the app found that because it severed its ties to the internet to save battery life, some apps that you might depend on for push notification like Gmail, did not work. You can go into the settings and override the BatteryGuru for each app, but it doesn't prevent it from severing that tie to the internet again down the road. If you depend on an app that uses push notification, perhaps you should be happy with the battery life you're getting now.
The app is available for free from the Google Play Store where the response to it has been overwhelmingly positive.
source: BatteryGuru via AndroidCentral