Just back from this tour - which was great. If you have the time/finance, I would recommend the Cambodia add-on, as none of us who did it were ready to go home after the Vietnam leg! The entire tour was well organised, accompanied by an absolutely excellent tour manager and super local guides with excellent drivers. All ran smoothly. Highlights for me were: the night on the junk in Halong Bay and the stay in Hoi An - which ( for the shoppers out there) is the place to get your silk tops etc. Don't wait til further down the line. Also US Dollars are accepted absolutely everywhere - but not two dollar bills in Cambodia.