As you said, it's not completely useless, but it doesn't work as it should. It does meet the low bar of expectation that I had from my previous bike (a Royal Star Venture). The needle sits on F for a long time, then drops quickly, and finally plummets when it gets down the the final quarter. When it hits empty, there is still a reserve fuel supply in the tank. For those of us who have been riding bikes with carburetors, no fuel gauge and a three-way fuel petcock, that reserve supply may make some sense.
I suppose this uneven behavior is due to the odd shape of most motorcycle fuel tanks. If we had level rectangular boxes to hold the gas, a steady gauge would be easy to construct. In this day of computers, an intelligent reading could be programmed, but Victory has not done the work. Just consider the inaccuracy of your digital read-outs, will be apparent.
All I can suggest is to do what I do. Know that when the needle starts to move, then between a third and a half of the fuel is gone. Quick progress of the needle after that will show the next third of the fuel supply being used. When it gets to the bottom, that's a good time to refuel, but you're not empty. That works for me, in populated areas, where there is always a gas station nearby. When I ride across the country, so that I may not see a gas station for a long stretch, then I start looking to refuel when the needle gets to the halfway mark - after about 140 miles. Just learn how your gauge actually reads and work with it.
2012 XCT (Blackbird)
Forged bars & JTD lowers
Stage 1 flash & Tri-ovals
LLoydz ATS @+6*, Air filter, Drop-in cams
VFCIII tuned by KevinX
Madstad with 13-inch shield
Tri-city Performance floorboard footrests
Corbin saddle & backrest
Cee Bailey's bag liners
Wolo Badboy horn
KuryAkyn Sabertooth lights