I have 1 DD who gets the GB to KEFW and another who gets the GB to KEHGs. They've never been left behind at their stop or anything like that and I've found the service to be very reliable.
There has been some 'silly stuff' at times, but the bus drivers are pretty good at keeping order and persistent 'offenders' are banned from the bus. And then the next day (after an incident) everyone is given a bollocking in assembly about bad bus behavior, with threats of the police, exclusions and other dire punishments!
I think that buses + kids - whether special services or 'normal' buses will always involve high jinks and tom-foolery of some kind.
My DD's find their bus time to be the high point of their day - and the morning journey is perfect for finishing off homework