Depends what the need is. How much data, how often. If they are going to be in country for that long having a local number and some minutes for calls/SMS might be useful, in which case just getting something on arrival, or having an eSIM for the first few days to get you going before you swap to a local SIM or eSIM.
There are many stalls at BKK both before and after immigration/customs selling SIM and eSIMs for all of the main networks and some of the MVNOs as well. They can also offer bundles for roaming within SE Asia if that is a concern.
Last trip I got an eSIM from Yo but only because one of their packages matched the unusual mix of countries I needed access in, so one eSIM could handle all the places I was visiting, and I was going to have access to local WiFi in most of my accommodation so data usage wasn't going to be so high.
The one bit of advice o would add is that the APN settings that come with the eSIM are not necessarily going to be correct. So get whatever the details are for the eSIM providers APN before you travel - they can also reconfigure themselves to be wrong each time you cross a border and switch to a new network....