What are people's experiences and tips for train travel from Bangkok to Kuala Lumpur?

Traveling from Bangkok to Kuala Lumpur by train is a lengthy and often uncomfortable journey according to various experiences shared in the comments. Travelers need to be aware that they cannot cross the border on one train; instead, they must undergo border control at the Thailand side and then board a different train in Malaysia. Some travelers highlight the expected duration, anticipating it can take upwards of 20 hours including stops and necessary transfers, with a notable portion spent waiting for customs and changing trains. While some enjoy the adventure and the sights along the way, many recommend flying as a more convenient and time-efficient option. Overall, while the train rides can offer a unique experience, they’re often characterized by long travel times, the need for frequent transfers, and varying levels of comfort—from air-conditioned sleeper trains to challenging conditions on cheaper services.