GPS and a fuel flow computer are 2 of the greatest tools I ever added to my plane.
Both going to and coming home from Clinton it was so nice to be able to look at the ETE on the GPS then check the time remaining on the FS-450 and see how much time I would have left upon landing at my destination. A wonderful reassurance as to how the flight was progressing and not having to do the calculations myself allowed me to enjoy the flying more.