tbh I usually get a good 5G signal where I go near kabin buri on the 304 but its fairly well built up but if you're trying to contact someone in a very isolated area it can be a bit hit and miss I use True when I'm in Thailand so does my partner and not any issues
in prachin buri the office computer for the TM 30 doesn't update the computer next door when doing an extension you have to take the printout and it's entered manually