AFFF leaves a smothering and wetting agent behind which both cools the fire area and prevents re-lights. The down side is it's a big mess, can cause difficulty getting out of the car, and doesn't "spread" so if the fire isn't where the foam goes, it don't go out. AFFF's big strength is killing liquid fires, it forms a "crust" on the liquid that locks it our from air and to some extent ignition source. However it is NOT non-conductive so it's basically AB only with a strong leaning on B. DJ safety makes an SFI rated Cold Fire system which cleans up easier and is supposed to be non corrosive and may be a better choice than other AFFF systems. If you go AFFF be sure to put in some solid anti-slip in the footwell and such because the stuff is basically soap.
Novec is actually a volatile liquid which sprays as a mist. It's completely non-corrosive, non-toxic as is or after it breaks down putting out a fire, and is supposed to be basically an immediate quench. It also cools from adiabatic expansion as its sprayed out of the nozzle, but may not cool things off below ignition temp. As it forms a gas that gas is heavier than air and pools which may or may not go where the fire potential is. Also in a moving car it can be diluted by the slipstream and air currents inside the cabin so coming to a stop first is a better bet. NOVEC and FE are non-conductive and so are suitable for Class C electrical fires, but they are least effective on Class A since the Class A can stay hot and smoldering when the Novec dilutes and dissipates. Also they Novec and FE work best in contained environments.
You wan't metal tubes. Is plastic even SFI or FiA rated?
The more nozzles you have the less agent comes out of each nozzle. a 5 lb is at its limit with 2 zones. a 10 Lb would be better for 3 zone.
The guideline is for under the hood you want 2 nozzles so that you cover both aspects of the engine since you won't know if the say left front or right rear of the engine is what's on fire. For the driver it depends on the system whether 1 or 2 nozzles is best.
In Car, especially with the power still on, A Novec style unit makes more sense given you have electricity going on in there. Also an accidental discharge only hurts the wallet. Foam has the benefit of dousing you with a fresh coating of flame retardant, but you'll want to get that electricity off quick. Foam also makes a hell of a mess, and if it gets in the engine, it's done. Also Foam freezes so add that removal inconvenience/chance for an accidental discharge into the equation.
Basically, if you think your car is going to hose the hell out of you and the ground around the car with gas and oil, Foam is better. If your idea is to add time to get out of an on fire car, with full extinguishing being a secondary consideration but one that leaves most of the car and the electronics usable afterwards, the Novec FE system is better.
If you know your team will set the damn thing off by accident, definitely the Novec and FE. No matter what an accidental discharge at the event is a weekend ender (unless you have a spare bottle) but with Novec only your ego and wallet will be ruined, not your engine, chassis, and electronics too.
Mistake By The Lake Racing (MBTL)
88 Thunderbird "THUNDERBIRDS ARE GO!"
A&D: 2014 Sebrings at Sebring (NSF), 2014 NJMP2 Jurassic Park (SpeedyCop), 2012 Summit Point J30 (PiNuts)
2018 Route Sucky-Suck Rally Miata.