Clean agent stuff is good for interior fires or other contained spaces. But outside of small fires where the agent may cool things enough to prevent re-ignition, they're utterly worthless for engine bays and other open spaces, as the agent can simply drift / blow away. When that happens, if there's still enough heat, the fire will re-ignite and you're back to square 1. Foam or a dry chem of some form is much better for open spaces like that.
Ideally, carry a clean agent and a foam or dry chem that way an interior fire can be resolved without a huge mess but you've still got something that can either coat or cool a fire in an open space and better avoid re-ignition.