Unfortunately I have some experience of a fire on a Boxster and the effectiveness of fire extinguishers.
I bought a couple of 600ml extinguishers. They ran out in seconds when called upon. If you have an engine bay fire you may as well just walk away and not bother. The engine bay has no access so you can't be effective with an extinguisher. The best solution would be a motorsport style system with nozzles placed inside the engine bay and also a hand held one for a fire somewhere else.
The fire brigade couldn't even put mine out.
