Corey, that looks like a very good choice. Three types of extinguishers can be useful for vehicles - dry powder type (ABC), halon (clean-agent), and foam (AFFF). The latter is for flammable liquid spills (such as fuel on the ground) so may be appropriate for larger specialized vehicles carrying large amounts of auxiliary fuel that may spill or for racing applications, but not as applicable to us. The powder is economical and depending on the type can put out fires from solids, fuels, and electrical but as you mentioned, it can be quite a mess. The clean-agent (Halon) type is a liquid stream that gasifies when it is deployed, and fights the fire by displacing oxygen. Therefore it will work best in confined areas such as inside a vehicle or in an engine bay. If you want the best of both worlds, carry a halon unit for application on your vehicle and a powder unit (ABC) for fires outside of your vehicle (camp site, public hazards, etc.)
HERE is an interesting article on vehicle fires from Off-Road.com