Like you, I try to avoid low cost carriers like AirAsia, but sometimes it's the only option for a direct flight.

I've found a lot of variability with enforcement of baggage rules. There have been times when my carry on has been weighed at check in. Sometimes I see them doing it at one check in desk but not at another one. They will almost certainly charge you if you're over the checked baggage allowance by more than 1kg (you may be ok if it's 20.9). The baggage rules are specific: "If you have purchased two (2) pieces, 1 bag weighs 25 kg and the other is 15 kg. You will need to remove the extra 5 kg from the 25kg bag and add into your baggage that weighs 15 kg, so that each bag weighs 20 kg." It is cheaper to buy excess baggage when you are booking your flights.

Interestingly, if you have no checked bag you can get your boarding pass on the app then go straight to the gate. They never seem to check carry on bag weight at CNX at the gate, but they regularly do at the check in desk.