Michael,
I originally had the JPI 760 w/out FF option. I later decided to clean up my panel, removed the shadin FF, and added the FF to the JPI 760.
I use it all the time, during runup, and when I set up cruise, and anytime I try to calc TAS, also it gives me gallons used, and remaining, so I always know what I have left.
I love it, the FF,
steve