<<You can trial half a dozen types by different manufacturers and get no consensus back from ATC as to which they want>>
Not the way it functioned when I was at work! We were given several to try and a folder was provided for comments. At that time I still knew some Tels people at MoA HQ so I asked them what they knew. They were surprised that we were being invited to trial several types as 3000 Astrolites had been purchased and were waiting at the store place at Aston Down for distribution! I put a note in the folder to this effect and was marched smartly down to stand on the boss's bit of Axminster where it was explained that I had wholly the wrong attitude!!!!