These "group portraits" are for you to compare shapes and sizes and get a sense of what would work best for your space, work, and your client group.
I am advocate for choice of trays which may benefit your working environment, however if there is nothing available that suits your requirements please email Chris at artisandtrays@gmail.com and I will assist you wherever possible.
Having at least 2 trays is useful to always have a fresh tray if a wet play session has left a tray flooded.
"Rehearsal of the possible" also benefits from a second tray to provide a fresh space for your client to create a completely new sense of possibility for their processes.