I came to say the same thing. The "build together" mode is super fun. Everybody can go at their own speed (without me dying inside watching my 7-year-old trying to figure out things). If you are faster, you build more subassemblies, that's it. Everybody is busy.
The kids particularly enjoyed the moments where you have to exchange subassemblies: "I need this from 'popcorn'!" "I need this from 'astronaut'".
When the kids got tired, subsequent steps were assigned to me as if nothing had happened. I am guessing there's a DAG of tasks (to build subassemblies), and the tasks just get picked up by individual participants.
10/10