Regarding Android 5 and higher: Only rooted devices can enable/disable mobile data using apps. Non-rooted devices can only schedule Wi-Fi, Bluetooth and the ringer sound/vibration. If you don't know what rooting is you don't have root and won't be able to schedule mobile data.
Network Scheduler is completely safe to download. Mani Mahler has developed the tool that falls into the Productivity category. According to the latest info, this application is rated 3.3 on Google Play.
Over 10K users installed the app and its latest update was launched on Jun 14, 2017. It's free to download the installation package of Network Scheduler, also, you can check out users' reviews on Droid Informer.
According to the users’ comments, the plus of the app is battery optimization.