Not correct. The main purpose of IDP is to have a standardised format which is in only a few languages. Thai DLs are in English and Thai. IDP isn't in Thai unless you get one from Thailand
It's true that not all LPG systems are the same quality, and it's also true that not all are properly (i.e. professionally) installed and/or maintained. I went for the best quality brand, had it installed by a specialised garage, and have had it regularly serviced. The point was about people making generalised comments rubbishing LPG as if it was universally problematic, or dangerous. Every taxi in BKK now has or seems to have LPG and how often do you read about them blowing up? It's also worth noting that the government now require an annual inspection, which is a change from the previous system which required only 5 yearly inspections.
7 years now with LPG conversion from Energy Reform, regularly serviced, and no problems. Some people just spout garbage without having a clue about the facts