[Gen1us2k]

1. It won't be working on stock devices, unfortenately. It's library to integrate to your android application

2. Extra calculations don't consume as much battery as GPS and with this technique we use GPS less often. In other hand we use accelerometer and magnetometer. I tested this by eye :) and didn't find big difference between GPS only solution and presented solution. But as written in article - it doesn't accumulate coordinates.

3. Android already has similar filters. They use Kalman filter and many interesting things. See here : https://android.googlesource.com/platform/frameworks/native/... and other files. They did really huge work here :)

[londons_explore]

For 1., on android you can have third party location providers I believe, and then any app could use it.

[Gen1us2k]

Yes, but you need to specify coefficients somehow for that and add calibration step.