We used them once, back in 2005.
You do need to book up ahead if you want popular dates/routes
I would use them again if I had too, but frankly I'd rather drive myself.
We found the pick up (in our case near Dartford) was more or less on time,
I guess as we are 'only' about 150 miles from the start and they have a specific ferry time to make the UK pick up timers were fairly good
Coach travel:
Personally I'd avoid it given the choice, but with a bike and a budget, trains are no longer an option and planes are no better
But by the standards of coach travel they have good double decker coaches with airline seats, loo, tv, drinks, snacks
We were dropped off at Orange (near Avignon), other than remembering it was before dawn, I don't remember if it was on time or not.
Coming back was a different story:
We were picked up in Saintes (near Bordeaux), it was supposed to be early evening, we ended up sitting for 4-5 hours through the night in a lorry park, thankfully the weather was fine, but not a good experience.
After a few calls to head office, they did start to keep all the people advised on how late the bus was running by text message.
Given than mass text technology and apps are now available, I would imagine they must have an 'ETA' app by now, so that you can see where your bus is.
One couple on our bus back had given up and checked into a hotel, who were then woken up at 5am to say the bus was outside, they got on board home, but their bikes had been locked into a storage room to which the night staff had no access. I've no idea how or when their bikes eventually got back!