Pineapple Metronome is a minimalism application that provides an out-of-box easy-to-use metronome application. Just spin to adjust desired BPM, and use the ON/OFF button to toggle metronome.
This application doesn't contain any ad or in-app purchase, doesn't require any unnecessary permission, just a clean metronome application.
Pineapple Metronome is a Free (as in Libre) and Open Source application with the term GPLv3. You can obtain the complete source code at: https://github.com/BLumia/pineapple-metronome