The xiao board snaps in place just like the one key version, and the battery sits in the void under the second key. The 6mm push buttons seat snug in the bottom panel and are held in place by the supports on the side once snapped together.
The author remixed this model.
This model extends the one key model to a two key model with space for a battery and a couple buttons on the bottom side which sit flush. One can be used to clear Bluetooth bonding and the other to reboot the board.