Another couple of data points. Weekend trip to EU. Booked expresstest at T5 for inbound pre-departure LFT before outbound departure. Had booked expresstest for Day 2 PCR also, but changed to HALO on reading this thread.

Arrived at departures expresstest at time of appointment (noon Friday) and joined a long queue. There was a half-hearted attempt at sorting people by booked time, but it was pretty inefficient and not at all socially distanced. We had a 40 minute wait and the test itself then took less than a minute. Results 37 mins later. PCR queue was much slower moving and a lot of customers there clearly not satisfied. When we got back (T2 arrival and transferred airside to a deserted T5 - 4pm Sunday), there was a sizeable queue at the arrivals expresstest, so glad we avoided that.

Waited for less than 5 mins at HALO. Self-administered and out in a further 5 mins. Results six hours later. Would definitely use them again.