UPDATE regarding CPU usage for Android Oreo and up. So Android Oreo added yet another restriction disallowing access to the CPU usage stats. Thus, CPU usages unfortunately won't work on devices with Android Oreo. I have released a beta version of the app accommodating the rooted Android Oreo devices where it should work just fine.
It's free of charge to get the .apk file of Simple System Monitor and you can take a look at users' reviews on Droid Informer. This application installation package requires 3 MB of free space to run on Android 4.0 and higher. According to the antivirus report, the app is safe and secure. Darshan Parajuli is the official developer of this application which can be found in the Tools category.
The latest update of Simple System Monitor was launched on Feb 21, 2018 and the app has been installed by over 0,5M users. According to the latest data, this application is rated 4.2 on Google Play. Samsung and LG users highly appreciate Simple System Monitor.
Some users suggest that the main advantages of the app are a simple UI and useful features.