According to Yochanan, an X-Treme Notebook is one which has a left and right side flap each functioning as a pocket. They come in most sizes. “Pro” means it has a Reporter Notebook and an additional Field Notes on the right hand side.
I have a Desert Storm Personal X-Treme Bi-Fold and a Fantasia de Fleur A5 X-Treme Quadfold Pro.
Both are unusual, limited edition leathers. The A5 is a brick and heavy when full but it is, in essence, a portable office. You can collapse it and use it as a knee-desk, if that makes sense.
The personal is much more small and compact as well as lighter but does not have the ability to carry as much, obviously.
I love them both! Yochanan is a true artist!