One odd thing is that advance seat selection for an AC ticket doesn't work on their web site. Their email support can't/won't do it. Their Facebook support can't/won't do it. They gave me two email addresses of a company in Thailand (because my flight starts there, I guess) to contact for seat selection, but neither of them bother to even reply.

That's just the start of the awfulness. The check-in agents in BKK can't print Bamboo boarding passes for the next sector and standard transfer desk agents at SGN can't print Bamboo boarding passes either. You are stuck in transit hell (no working WiFi, no shops except for SIM cards, no food, no drink) until Bamboo agents turn up. In theory, that is 3 hours before departure, but they are late and then dither around. They don't even ask you what your seat preference is and a 1 min job takes over 10 mins, when you've already been waiting for 2 hours.