They really are the same. The only "real" difference in my eyes is the technicality involved in the Dual angle system.
The dual angle does more than set the MB position, but sets your pin to val as well. It may not dictate how early the ball will roll, but will dictate the type of backend you get which is pretty important as well. Just saying "I have a 4x4 layout and my Pap is this", is unfortunately pretty generic, as this way of stating it is only saying "My pin is 4" from pap, and my mb is 4" pap". For me, this honestly tells me nothing. This could be a strong layout, this could be a weak layout. It depends on the pin to val.
Now, I'll take a ball that I have and say that I have a 55* 5" 65*
http://smg.photobucket.com/albums/v690/Phoenix_RsX/Arsenal/?action=view¤t=IMG_0001.jpgAfter reading Mo's dual angle lecture on his page, this tells me that the 55* is going to give me medium length, with the 5" pin creates large flare-more of the ball making contact with the lane. The 65* is going to give me sooner, yet continuous backend. And this is exactly what I got.
Knowing what I know now, they are all the same. However, pro shops for the most part(in my experience) do not take the time to watch your style and help you pick the best layout for your style or explain why. They seem to be more concerned with getting your money and tell you what you WANT to hear and not what you NEED to hear. Yet, I prefer going the DA route because it's honestly easier for me to understand and I know exactly what look I'm going to get and when it's best to use it.
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http://smg.photobucket.com/albums/v690/Phoenix_RsX/Arsenal/Uroboros will be released into the atmosphere, ensuring...complete...global...saturation.