South Wales coach link
I've looked at the First Greyhound coach link to the airport from Swansea, Cardiff, Newport, UWE Frenchay campus and Bristol bus station that commences on 11 March and the operators seem to be giving it every chance.
There are 15 return journeys to/from Bristol Airport each day with nine of them starting and finishing at Swansea.
The other six return journeys commence and end at Cardiff. There are three in the early morning beginning at 0320 from Cardiff and calling at the above en route stops and three in the late evening/early hours.
These journeys at 85 minutes from/to Cardiff are speedier than the daytime ones and are obviously aimed at the concentration of early morning departures and the later evening arrivals.
It's almost a 24-hours service, like the Flyer (which is). Only time will tell whether it becomes anywhere near as successful.