When I did Brands GP last year they had four groups on 20 min session. Downside was the number of red flags throughout the day. I must have lost at least one session due to stoppages, and that really pissed me off. As an example they had 3 riders go down in one pile up at Druids, which wiped out half of one of my sessions.
Rockingham marshaling was way better IMO, plus we seemed to have less twats out on track that day. There were plenty of incidents but they kept the sessions moving under yellows, and I only saw one red flag all day. The MSV control and marshals seem a bit jobsworth, bringing out red flags for the most minor things on track. Bit of a wind up when you've spent over £200 to ride the GP layout.