Good point. An individual 30 minute session may not be best for everyone. That said, it is low cost, low risk, and worth a try. My experience is that most people with significant histories of trauma are able to meditate by themselves. The setting and duration can be varied. Guided meditations can be helpful. And if it feels uncomfortable, it is easy to just stop.
It is great that there are group supports for people who do better with a group. And many people seem to do well with a weekly group for support and individual sessions in between. No single solution. Trial and error can help people to find a practice that works for them.