I've been interested in these off and on.  The argument against them has always been that there's so much airflow through the cowl, that Halon might not be effective.  We still have Halon in some of the MRI suites, but those systems are automated to close doors, and turn off any ventilation systems when they're activated.  I know these types of systems are used in race cars, but I imagine they're usually activated after the car as come to a halt. 

 
I'd be interested to hear some thoughts on this.

 
Hi Rusty;
        I ran a 3/8 tube drilled with 1/8 holes every 4" which follows my fuel system. It is crimped at the end and attached to the F/W with a bulkhead fitting. On the cabin side I ran a 1/4 hose from this fitting to my fire extinguisher mount. I removed the plastic nozzle from the ext. and replaced it with a tube fitting. I leave the hose connected finger tight and ready to discharge into the engine compartment if necessary. It can be quickly removed to use in the cabin if needed. I just use a dry chem extinguisher, as Halon is illegal (and$$$$) in Canada. Will this work? I hope I never find out!

        As far as too much airflow to be effective, consider jet engines. Much more airflow than we have and yet it works instantly, however it also releases the entire extinguisher contents instantly.

S. Todd Bartrim
Turbo 13B
RX-9endurance
C-FSTB
http://www3.telus.net/haywire/RV-9/C-FSTB.htm

        "Imagination is more important than knowledge"
                                        -Albert Einstein