Got on fine, thanks AnalogueAndy. No hold ups at all when I was there. I left Cardiff at 6.30am, hit J19 on M4 at around 7.30 as advised, and was parked up in Broadmead car park at 7.50. However, shock of the day for me was £16 parking at Broadmead. Crikey. If you ever come to Cardiff, I’d recommend the car park at the old Cardiff Arms Park (next to Millennium stadium). It’s £5 all day there and right in the centre too.
I suspect with rush hour commute there’s a window before the masses arrive where the journey is relatively clear, but 30 mins later and you’ll be held up and crawling an hour late.