Just as an update, I am currently waiting for a flight to Dubai. Monkey class sadly. First time through BKK in a few months and I have to say it just keeps getting better.
15 minutes from check-in to security, getting a multi entry re-entry permit and through immigration.
Security looked busy but was really quick - the new system is much improved in terms of passenger flow. No need to take laptop out of bag or take off watches, belts, shoes.
Re-entry took just under five minutes from me approaching the counter to having my passport back with a multi entry re-entry permit. Because I had done that I wasn't allowed to use the auto gates and was directed to an IO but there were no people in front so took about 15 seconds. Loads of auto gates now, no queues.
Milling around the place is busy and I expected the worse, but it was a breeze. Well done AoT.