One of our dogs, a springer spaniel, got fuzzy on her liver patches while the white parts of her coat stayed smooth

She looked like we'd stuck fur fabric patches to her :D - very strange :D :D
A Coat King would definately make taking the fuzzy stuff out an easier job, especially if it won't come out with pulling. They only cut the top coat if they aren't used properly, You must comb through first, and you
must follow the direction of the coat growth and the way it lies. Strangely, the harsher/smoother top coat seems to glide through and the fuzzy undercoat gets caught. Its up to you how many passes you use and how much you take out, as long as the one you're using isn't too fine for the coat it should work fine. The ones I got came with easy to follow instructions.