Preface: I am a 'hard marker' and very critical where I think the tour operator could be better. Having said, I have absolutely ***NO*** substantive criticisms to make after our 2 week tour, starting in Hanoi.
Our guide met us at Hanoi airport late at night (having met other straggling incomers during the day) and this set a precedent for individual and collective caring under his shepherding for the next 2 weeks -- nothing short of superlative. From Florence Nightingale to facilitator to problem-solver to advice on restaurants to guiding itself, Thien's leadership was beyond-ordinary. We all felt very well looked-after and safe.
If I have a criticism, it could be the micro-management of one's time so as to get everyone organized for each side-trip. However, if we weren't time-managed, we would never have seen and experienced as much of the sites and the local culture as we did in the time available. Take one's pick!