My comment was from observations in the sim in a realistic working environment. Thanks for the info on 'behind the panels' electrical connections. The F bug is displayed on the speed tape immediately the flap lever is extended; i.e. before the TE flaps move. I now understand that there is also a sensor on the flaps to detect any 'disagreement'. I wondered if that might have been simplified by using the TE gauge, but that would not work in a total AC failure when the gauge is not powered. Thanks for the info.
The gotcha was demonstrated by crews who did not monitor the TE gauge and continued to extend the flap lever and bug the F speed without noticing the TE flaps were frozen. That is where I used to hammer the point that F bug is from the lever not the flaps themselves.