Sleeper buses are exactly what they say they are. They are buses, which theoretically, you can sleep on. They are an economical mode of transport, as you don’t have to pay for accommodation, a great place to meet other travelers, and perhaps if you are unlucky, you might pick up a few unwanted bugs like hair nits.
When I was in Vietnam I travelled by sleeper bus a lot. Unfortunately, my experience was not the same as on this video. After 3 weeks of hopping on and hopping off sleeper buses I can definitely say that the best approach to the sleeper bus is to take a cocktail of sleeping pills, Valium and Jack Daniels at least 3 hours before you get on. All in all, they are as cheap as chips but they are not a good substitute for a bed and a duvet. Listen here to a guy from Australia talking about his experience.