I went to the one in Cwm near Ebbw Vale.

Rang around 10. No availability in Abercynon. Earliest appointment 5 in Cwm. Your given a half hour slot. Staff guide cars check you have an appointment by holding a sign , scan your appointment barcode. Some have mobile phones which you ring and they give you instructions. Theres then a drop off point for your test.

There was a car leaving as we arrived there was also cars there and arrived after. It didnt appear busy but with you being allocated a half hour slot im not suprised. Im not sure how many slots they have for each half hour.