Fuel Sending Unit?

I have just put a new electronic engine monitoring guage on my Falcon.
It allows for connection to any fuel sending units for fuel
monitoring. I've talked to just a couple of people who have told me
that a fuel gauge is undependable. That puzzels me because you can't
buy a car without them nor have I ever been in a commercial plane that
didn't have one. My guess is that it all depends on the sending unit
used. Can anyone reccommend an inexpensive yet dependable fuel sending
unit?