Megabus seems to have a bit of shortage of vehicles in Cardiff as I have taken 3 M7/M10 journeys between Cardiff and London and they were all operated by Edwards Coaches, or is it a routine arrangement?
1940 From Cardiff and 2100 from London Victoria
The boarding stop at Cardiff is not that awkward as it is still in City Centre but indeed it is less noticeable when comparing to the NX stop at Central Bus Station.
I found that the interior of B9Rs look lusher than the Megabus Vanhools as they are equipped with Fainsa leather seats which I personally prefer. Yet it is more exciting to ride on a double decker on M4 and they are not bad to sit on for a three-hour journey too.
Megabus usually finishes a return journey from London to Cardiff via Bristol UWE and City Centre in 3 hours and 20 mins while NX took the same time for a direct journey and is usually cheaper than NX eventhough with coach card discount applied.