There are varying degrees of success with other devices.
Try the following to see if the app works:
If you are on android 4.2 or below:
Go into your phone settings->accessibility and switch off and back on lightflow in the list.
If you are on android 4.3 or above:
Go into your phone settings->security->notification access and switch off and back on light flow.
For all android versions:
Go into your phone settings->display. Make sure "pulse notification light" is checked (if the option exists - you may have something like LED's or Lights instead)
Switch off your phone with the power button. Then switch it on again.
Go into lightflow -> general settings and make sure direct mode is off.
Then go into notifications -> missed calls.
Set the color to "red"
Set the flash speed to "fast"
Switch off your screen and wait 10 seconds.
Does the LED light up?