I flew Air Asia in May and wanted to share some impressions and answers that I could not find before my flight. Hope this is helpful.
Itinerary was HKG-DMK-LPQ (Hong Kong-Bangkok-Luang Prabang)

1. This is definitely a low cost carrier. There are no perks that might lead you to believe otherwise.
2. The seat pitch in normal economy seats is knee crushing. I had true pity for the people sitting in those rows.
3. But, the cost to upgrade to the exit row is absurdly little (e.g., US$12 or less on one leg). I cannot understand why people would not spend so little to get out of such cramped seats. Shockingly, the exit rows and all of the preferred seats were basically empty while the seats at the back of the plane were completely full.
4. There are four groups of seats on the plane
   1. Bulkhead (row 1) which had more leg room on one flight, but standard legroom on another flight, seems hit or miss. I could not get an answer before my flight whether these seats had more legroom. My impression is that it is dependent on the specific aircraft.
   2. Preferred seats at the front of the cabin (these had standard, knee crushing legroom. The only official advantages were pre-selecting seats and being at the front of the cabin. Unofficially, since so few people pay for seats, you would have had a lot of extra room around you.
   3. Exit rows, with significant legroom
   4. Standard seats
5. Important: If you didn't pay for better seats, the flight attendants would not let you sit in open seats. As a result, the front half of the plane was nearly empty, the back packed.
6. There were signs everywhere about the strict weight limits on carry-on bags and scales at the boarding gate, but our far overweight rollaboards were never weighed. (Our bags were not huge, but certainly heavy.) I do not know if this had anything to do with the fact that we purchased exit row seats and had priority boarding nor do I know if they weighed any bags at all. We did check in online to avoid going to the ticket counter where this might have been an issue.
7. We bought our tickets from an online travel agent (Kiwi.com) as a single itinerary straight through with a connection in DMK. However, they booked it as two separate PNRs, a fact we did not know until the reservation was ticketed. Apparently, Air Asia will not ticket a connecting itinerary unless booked directly with them. This became a problem when we landed at DMK and the massively unpleasant Air Asia ground staff person policing the entrance to security for connections refused to let us through (despite the fact that we had our connecting boarding pass, having checked in online). She forced us to go through passport control, back up to departures, back through passport control and through security. She was not sympathetic that our inbound flight was late, cutting our connection time. Thankfully, the staff at Thai passport control were lovely, and moved us to a shorter line. I expect that had we had checked luggage, this would have meant that we would have had to claim luggage at DMK and recheck. The checkin lines at DMK were horrendous, so we likely would have missed our flight. It remains completely unclear why the agent would not let us through the connections area. The online check in boarding passes were honored for the flight and at security and we made it clear that we had no checked luggage.
8. Besides the obnoxious woman at DMK, the staff were generally friendly.
9. DMK is a dump. I hadn't been to the airport since Suvarnabhumi opened.

I only flew the airline because the timing and connections worked. It wasn't my first choice. It was a great value and, comfort-wise, the exit row was perfectly fine. The shenanigans at DMK were absurd and I do have some safety questions. I hope this is helpful for others looking for information. Sorry it took 6 months to post.