I know that Laos isn't in Vietnam, but arguably the easiest way to see the recently described Bare-faced Bulbul is by making a quick trip into Laos from Vietnam. I don't want to set a precedent for expanding the scope of this website beyond Vietnam, but I thought that information on how to do this might be of interest.
Aside from the endemic bulbul, Sooty Babbler is easier to see in Laos than in Vietnam. In addition, going to Laos to see it invalidates the need to visit Phong Nha Ke Bang. Red-collared Woodpecker is also much easier to see in Laos than in Vietnam. So visiting birds could add these three species to their Vietnam trips by just visiting Laos instead of Phong Nha Ke Bang, as long as they get a multiple entry visa for Vietnam.
Laos is expensive to fly to, even from adjacent countries, return tickets to and from Vietnam cost $400, and it is very easy to visit using public transport. So that is what I did. The total cost including transport, accommodation, food and visa was just under $100.
I began by taking the overnight train from Hanoi to Vinh arriving at 4am on Saturday morning. You could equally travel north from Da Nang to Vinh overnight, if that was where you were based. The first bus to Trung Tam (the border town in Vietnam) leaves at 6am, and from there I caught a bus to Lak Sao, in Laos. The border crossing was uneventful aside from a Nepal House Martin (sadly not on the Vietnamese side), and once in Lak Sao it was easy to hitch a ride along Highway 8 to Na Hin village.
Just after lunchtime I arrived at the Mi Thuna Guesthouse in Na Hin village. I hired a motorbike from the guesthouse and drove up to the viewpoint described on Stijn de Win's website. After about an hour of scanning with the scope I located a trio of distant Bare-faced Bulbuls perched atop the karst. After another hour of waiting I headed downhill to an area where the karst is next to the road. A short walk along the road quickly produced a party of 10 or so Sooty Babblers flopping around on the rocks, giving great scope views. I returned to the viewpoint and spent the rest of the afternoon getting increasingly good views (ending with very good views) of trios of the bulbuls (although only two trios may have been involved) and found a troop of seven Laos Langurs before dark.
An early start on Sunday was curtailed because my motorbike had been boxed in by a 4x4. I improvised a ramp out of some planks, drove the bike up onto a thankfully very low wall and got round the car. At 6:30am I arrived at the track to the pumping station at km 48.3. However, on reaching the small trail just before the pumping station I found four kids with guns shooting at anything that moved. I quickly abandoned this plan and instead tried a different trail located approximately 200 meters before the pumping station on the left as you head up hill/away from the road. This trail descended steeply into good forest.
With the ipod dead I tried whistling an imitation of Stijn's Red-collared Woodpecker vocalisation, a sort of explosive kwaa!. After about 150 meters of walking I heard a response, coming from the forest floor to my left. I then heard what sounded like a Blue-naped Pitta vocalisation coming from the same location. Keen for a bit of two for the price of one action, I began to imitate the "pitta" as well. A bird flew up to a branch c. 1 meter off the ground from the direction where the sounds were coming from - it was the woodpecker. This bird soon flew off (and continued to make the sound like Stijn's recording), so again I whistled the Blue-naped Pitta type noise. There were no more pitta type sounds from the forest floor, instead the woodpecker flew in to a tree 20 meters up and showed well. Twice, Blue-naped Pitta type vocalisations came from the location where the woodpecker now was, high in the tree. For obvious reasons, I then gave up trying to find the "pitta" and went back to the guesthouse for breakfast. It was 8am.
After all that enjoyable and satisfyingly successful birding, the only thing left to do was to retrace my steps to Vinh. I did this and took the late train back to Hanoi. This arrived at 5am, in time for work.