Halon is the gold standard in fire suppression. However it's manufacture was prohibited under the US Clean Air Act od 1994 as it is an ozone depleating Bromated Flurocarbon. It is still manufactured in some third world countries. It is NOT illegal to possess and use on actual fires.
In fact the FAA requires up to 5 1211 Halon units on all heavy commercial airliners.
Halon 1211 is a pressurized liquid most commonly found in hand held FE's that is a non-conductive, oxygen robbing agent that leaves no residue as it turns to a gas at normal atmospheric pressure.
Halon 1301 is a pressurized gas used in gas flooding fire suppression systems.
Halotron is a synthetic substitute for Halon, a 2C3FC. It is fairly new and is supposed to be as effective as Halon however it has not been around as long.