Just returned this week from taking the overnight train from Hanoi to Sapa and back.
We took the King Express train and used the VIP compartment (private 2 bed compartment vs usual 4 bed compartment).
What a mistake!!! Avoid this train if you value your life.
We were up all night while a piece of metal from the carriage slammed against our compartment with the force of a sledge hammer. We feared we would be impaled when the metal broke off or that the train would derail. An overnight train ride that is so dangerous that you can not get any sleep is not pleasant, to say the least.
This happened on the initial trip to Sapa and was far worse on the return trip to Hanoi 2 days later.
Clearly, King Express does not perform any maintenance on their cars and their train is a disaster waiting to happen.
Avoid this train. We would have avoided it at any cost if we had known what we were in for on our journey.