So, to whoever might be interested, I decided to go for My Hoa lagoon
(Vietnam) from 25th of November to 22nd of December 2019 and this is my very short report:
I got there (Saigon) from Zürich (Switzerland) super cheap (600 EUR) with Edelweiss Air (luggage is no problem with them). After a few days in Saigon I took a train (yes) to Phan Rang - Thap Cham (around 3 EUR) and a cab (around 15 EUR) to my hotel (Phan Rang Kite Center, see URL above). On my way back I flew from Cham Ran airport to Ha Noi and back to Saigon (the national flights are basically for free, 20 EUR if you book ahead of time; the flights are reliable, though Vietjet has quite a reputation for being late - and they live up to the expectations).
The place is really nice, the hotel rooms are very new, clean and huge. I stayed on my own so it was a bit more expensive for Vietnamese standards, but if you stay with two people, 25 EUR a night incl. breakfast is a steal, giving you live on
the kite spot.
The wind at the spot was blasting around the clock
during my stay, though a bit choppy at times (mostly getting better after noon). The temperatures were very nice (never too hot, never too cold, no rain, few clouds). The water unfortunately was too shallow/non-existent during some days of my stay. Therefor, you should definitely check the tidal levels during the days you plan to stay before you actually book your trip. Still, even with no water around there is enough to do (cruise around on a motobike, relax on the beach, drive to Phan Rang, ...). There are unfortunately some hazards though, in my opinion the linked report does not emphasize them enough: You can very easily scratch your whole body on the coral remains (it is getting better indeed, but not good yet), hit one of the pipes going from the open water to the shrimp farms or smash into some concrete pillars holding them down so the pipes don't float (this is what happened to me) or get dragged over a reef if you're out too far. You should definitely wear booties (or be a more experienced rider than I am).
All in all, you will have a great time in the lagoon, especially if you check the tidal levels upfront (this will of course reduce the possibility of injuries dramatically). I'm still curing one of the bruises now, but I can recommend it still.
In case you have any questions, feel free to PM me or ask in the thread. Thanks at this point to all the other suggestions here