Scott,
When Cal and I began to talk about fire systems I told him something I found at the Fun Ford Weekend boards. Why the Ford guys,well because they race more than we do. FFW has also mandated fire systems in participants cars.There a many guys over there that have suffered fires , some at the tree some at speed.
With that said, Almost all fires begin in the engine compartment. After the fire is out,there's always the danger of re-ignition. Bare wires, scorching hot headers, turbos and electrical components will easily restart a fuel fire. Seen it many times on video and once in person.
A halon fire system is very effective and much better than NO fire system. But the wet foam system that I recomended to Cal in my opinion is best. The foam will kill the fire , but most of all stop the danger of re-ignition. It cools the hot exhaust and clings to everything.
Some will say "what happens if the foam gets under the tires" , well hopefully when you deploy the system you are not going to be on the throttle. You will be at the starting line or already trying to bring the car to a stop. The vehicle should come to safe stop if you keep a cool head.
Halon on the other hand is more likely to be dispersed and forced out of the engine compartment if the car has any speed behind it.Then you still have to deal with that hot set of headers and turbo.
Im no pro at this , but I did a lot of research in this subject. I have yet to purchase my own system, but hope to soon. Im glad that at least one of us made the move.