the picture of the catch can with the sight glass is what I had in mind. My saying its a lot of work and can be dangerous is you got to make a couple of holes in the tank then tap them etc. Some people will cut /weld on a tank with out a good cleaning of the tank first, the results can be very bad. Lot of the guys don't have the tools necessary for the mods needed. So if you will take off the gas cap and look inside the tank its fast and easy way to check for fuel.
Some of the choppers I've seen have the sight glass set up on the tanks.
If you run out of fuel in an airplane you become a glider depending on how high you are your chances of a safe landing will improve gives you more time to pick out a landing spot or more time to break out the bible and study for the big final test before the Uh Oh happens. Most all of the ultra lights I've flown if the engine would quit just about look straight down as that is how far your going to glide. to me they glided like a brick lots of drag and not much inertia at least on the few ultra light I've flown.