I have a teacher who developed a series of long tones to be done specifically with a "hoo" attack. It really helps establish the tongue level that you need to get the lips vibrating without articulating with the tongue. That is the most efficient postion. I have found that it set me on the right path for sure. I am not saying the "pooh" attach is wrong. It is excellent an tool, too. It all depends on what aspect of your playing you are trying to improve.
Two years and still can not get these damn attachments; most frustrating.... "pooh"