Class K extinguishers were approved as a class somewhere about 1997 or 98. They were targeted almost exclusively for commercial kitchens because of the changes of cooking styles to different types of fats and fat content.
Halon is also very much used in commercial kitchens, but expensive to recharge.
But considering all (like price $$$)...I'd advise EVERYONE to buy and use Dry Chem (class B) extinguishers. Once I worked with and saw how superior they were to all other methods in putting out diesel fuel and jet fuel fires in a training pit, there was NO QUESTION in my mind.