Don't listen to them, Nigel. I took the same journey from Morchit when I was there last time. I was impressed with the comfort and the punctuality. A few nutters on the road but that's what we expect in Thailand, isn't it ? Our bus driver was good but, unfortunately, I cannot remember the name of the company.
The family met us at Khon Kaen bus station with their 4 x 4 and I drove around Issan for three weeks. I returned to Bangkok by bus, no problems at all.
I think a lack of confidence in their own driving skills may be at the heart of those who tell you to fly. You drive for a living, I have driven nearly a million miles in my life, so we don't need to let the "scaredy cats" talk us out of doing what we want.
It makes you wonder about the validity of other advice given on this forum if there is so much uninformed bollocks written on this thread.