A lot are done in tubes, it depends on how many times the pattern changes. Sometimes tubing it is more work than not tubing. My avatar is an example of a bargello that is NOT tubed because of the constant changes.
I have her book too and before I attempted one of hers I took an online class at Quiltuniversity.com with Ruth Blanchette called "Bargello Seasons". In the class you do 4 bargello each one slightly different, progressing in difficulty. All 4 of the bargello in this class are done using the tube method.
The class is all online, the teacher sends you the instructions and you can logon to a board and ask questions and post pictures for her to give you tips etc. I highly recommend it.
My avatar was made in her second class "Bargello blues".