The developer rolled out a new version of Physics Toolbox Magnetometer on Sep 16, 2020 and over 50K users downloaded and set up the app. Adverts are a part of this application. Samsung and LG users recommend the app.
A free .apk file of Physics Toolbox Magnetometer 1.4.3 is available from Droid Informer and you can read users' reviews on this site. Prepare 2 MB of free space on your device for this app setup package and keep in mind that it works fine on Android 5.0 and above.
As users mention, the big plus of the app is a clean interface.