Just a free app to show speed in units of your choosing.
Requires only GPS permissions.
Source code is available under the GPL: https://bitbucket.org/nearwood/custom-speed/
1.0: First release includes MPH, KPH, m/s, ft/s.
1.1: Added a few more units. Changed launcher icon. Changed theme.
Improvements down the road will include custom speedometer size, more units, keeping the display active, etc.