Review from a student who took M 408K
He's a decent, average professor. He has a strong German accent, which may distract you from time to time but comprehension will not likely be a problem. The course is completely run by the department--he was only lecturing not making tests/homeworks. Dirr sometimes had issues understanding student questions, but then again most professors do. He did take the time to slow down and cover some basics, however the pace was still fairly fast.