Trusty
I am in the same boat as you at the moment. One of the instructors at my club said that there is a new TT book containing a JAR supplement. He recommended that I don't bother buying the new one as the new section is relatively small. The people at the club would give me the bits that I was missing.
I don't know yet how much more is in this new book because I haven't looked, but I would have thought that there is not a great deal difference other than new definitions etc. Maybe someone else could shed some light on this.
Good Luck with your exam when you take it.