Halon is a gas and works as well as CO2...I've used both. Advantages of Halon is that the fire extinguishers are much smaller, and they have a pressure gauge so you always know you have pressure. CO2 extinguishes are large and heavy by comparison; they don't have pressure guages, and the tank is supposed to be hydro tested every 5 years or so. Both types can used it as many times as you like til the charge is gone.
Halon types can produce nasty byproducts in the presence of flame, but so does burning fibreglass fuselages.. In either case, I'd rather not have a fire at all and never have to use it....