Can someone tell me the difference between this mod and the little glow indicator in my dash (02 F250 Lariat)?

 

The one on the dash lights for a pre-set amount of time and goes out. That is no indication of the glow plugs actually being energized.
The LED mod only lights if the load side of the GPR is energized and stays on as long as the GRP is energized. This can be up to two minutes.