Ended up booking everything a few weeks out, the prices didn't drop over the 6+ months period I was looking at and gradually increased - this was for June 2018

3 VN flights and 1 VJ flight
- VJ flight was late by 2+ hours departing, damn check-in girl knew very well the flight is late but didn't say anything even when I asked. The video board in Phu Quoc insists that my flight has already took off, found out the exactly delay time using flightaware
- Successfully used Optiontown on the VN's DAD-SGN flight. Since we were connecting to OZ flight SGN-ICN, I wanted the extra privileges in case of delays. As it turns out all VN flights were fine and on-time, and on the upgraded (US$ 25 per) flight we were the only J pax in a pretty large business cabin for a A320/A321 - 6 rows x 4 ?