Its small panel similar to the Android Volume control panel.
It’s very useful in case of: 
Volume button stops working.
Case/Flip Cover that hinders pressing Volume button 
And for friends like me, I always want to avoid pressing physical phone button to 
saving volume button from tearing off ;)Volume Button is exactly the same as Android Volume Panel.
1. Adjust Ringer Volume, System Volume, Media Volume, Notification Volume &In Call Volume
2. With the White Background and dark volume controls, visibility in sunlight are high.
3. Access any time without closing app. as its have optional Permanent Notification option.
4. Consumes NO battery at all

So light simple and easy to control different volume.
Material theme following Android designs and without any complexity & minimal Images. Its fast & smooth.