Speedtest.net is an internet speed tester available on iOS, Android, Desktop and Web.
The interface is semi material design meaning that it has solid colors, however it still uses gradient shading. There is a big Begin Test button and 4 other task options named Results, Settings and About. When you start a test it shows a giant speedometer and two charts named Download and Upload. When it finishes you have a option to restart or share the test and a button for removing ads. Swiping up reveals an easter egg.
I would give it a 5 out of 5 because it does its job well.
EDIT (2/21/2020): Fixed my atrocious 8th grade grammar.