This is excellent! I would love to hear more about the process you go through to design one of these.
The first thing that I thought about for the second box was how I make the lid. I didn't wanted the locking mechanism to be seen and I also didn't wanted to have a drawer like on the first Box. So I started with the locking mechanism and build the Box from top to bottom.
I had to think a lot how I can realise the "Undoing-mechanism". The piece that is moved at 0:34 gets unlocked by pulling up another lever. After you have moved it the lever can't fall down. Now some other moves are alowed that then again alow the piece to move again in another direction and the lever falls down (0:47). All moves can be undone now and the piece that I pressed inside at 0:39 allows the long piece that i moved at the beginning to slide to the opposite direction (1:02).
Thats a little bit of my thoughtprocess
For the first Box I only made chains, so that one move unlocks the next one. That was also used in the second box but it wasn't the focus.
Another problem is to fit the mechanism inside the box. The sliding pieces that look harmless on the outside are very branchy on the inside.
I used a paper at first to make a sketch but it was easier to just start building and sometimes correct or adjust some earlier building steps.