It's mission statement is:
Calibrator started as a J2ME app (J2ME development was annoying) and now it has been ported to Android (much smoother development). It was born out of the problem that devices were fragmented across many manufacturers and in-depth info (especially software) was hard to come by. When a manufacturer installs Android on their device, they target a specific version, for example Android 5.1 Lollipop. But there are anomalies in the individual libraries that are available. That's one area where Calibrator helps.
The app has been targeted at Android 2.0 and above so most devices should be able to run it. The older the device, the slower device, therefore tests take longer on older devices.