It is not because of all the old English translations that turn regular old davening lyrics into Shakespearian plays. Its not the abridged versions of davening that they use, only to tell you to go back to page 357 to find what you are looking for. Nope!!!
Birnbaum Machzors provide one who uses them with one of the greatest feelings of joy on Rosh Hashanah besides for that first bite into warm honey slathered raisin challah. In fact I would argue that the feelings that come from using a Birnbaum Machzor may even beat the honey slathered challah, gravy laden brisket and dip the apple in the honey song.
The great feeling I am talking about happens during every Rosh Hahsanah prayer in which the chazan is droning on and you are trying to find your place in the super complicated Birnbaum. When you eventually find your place which was lost in the first place because due to Artscrolls monopoly on the Jewish prayer book market- you come to the joyous realization that the chazan just skipped over a whole bunch of pages in your machzor.
I first realized that davening was way shorter then my machzor said it was during Maariv when they were busting out some of those responsive prayers about how God rocks and all. He does by the way, and I was lost of course because I was mad at myself for forgetting my Artscroll machzor. Of course most of the high holiday davening is spent turning pages and counting how much we have to go and the Birnbaum Machzor allows you the thrill of knowing we just skipped a whole bunch of davening is hard to compare to any other Rosh Hashanah feeling.