The car was adequate; we rode the same comfortable bus the entire way. The only thing I'd say is "aww" is that the air conditioning is on very high, even with the individual vents closed. This is the case almost everywhere in Asia. So, bring some warm clothing or something to cover yourself with.

The driver for this trip was very nice!

Honestly, the best bus ride I've had so far has been Mong Cai to Hanoi from 11PM - 6AM. Staff were polite and helpful, and unlike other rides, it was easy to sleep, because the driver wasn't constantly honking. I woke up at 4:30 AM in time for a bathroom break, and the facilities were clean. It's definitely a budget bed, but as a short queen at 159 cm, I was able to fit with my shoes and backpack. USB port works, and with the Viettel 8 gb/day plan, I had plenty to keep me entertained. Water is provided, and the only real negative was a loud auntie on her phone. (not much to do about your neighbours!)