I'm the one that came up with the term "Nordic" when I suggested Eric use that type of sauce instead of a tartar sauce in the thread where this was first discussed. I actually was thinking more along the lines of a creamy dill sauce since he had originally asked for a tartar sauce recipe.
But, Eric, if you do decide to go with a mustard based sauce using dry mustard, I'd definitely agree with those recommending Coleman's. The sauce we make to go with stone crab claws calls for Coleman's. We've made it with McCormick dry mustard when we couldn't find Coleman's once and it wasn't anywhere near the same. Coleman's is definitely the best.