Summary

There is a V3 version now with a more pleasant rounded finish.
Nice small box for the RPi Pico, any smaller and it's not going to be a box anymore.
The lid is very close to the BOOTSEL button and thin enough to allow using the button without opening the box ... you will have to remember roughly where to press.
The holes in the bottom allow you to use 1.0 mm round pins to make non permanent contacts.
There is a picture in the gallery showing a SD card wired up to SPI 0 with 1.0 mm pins salvaged from a DB25 male plug. Be careful with salvaged pins they need to be exactly 1.0 mm any bigger and they will not go in, any smaller and contact will be unreliable.
I happen to have requested to an electronics shop some 1 mm pins and received something around 1.1 mm : they don't go in the holes.