I have successfully installed the shim in my project and I think it is a fantastic solution to on off control of headless systems.
I do however have a couple of observations…
My hardware is RPI Zero W running Buster.
– Make sure you have turned OFF 1-Wire in raspi-config. If it is switched on, it will interfere with the SHIM causing it to malfunction. I do not know if it is possible to configure an alternative to BCM-4 but if not, it is a shame to have used this pin as it then prohibits the use of 1-wire sensors.
– In my implementation, to start from power off, I need to hold down the button for about 5 secs until I see the zeros LED go into the obvious boot flickering state. If I let go when I first see the LED on, then the boot just stops. This may be by design, just need to set expectations and perhaps avoid people thinking it is broken.
– In order to get the shim to fit when zero is in (even a low profile) case, then the headers are needed.
– This is not really a SHIM as the board is not offset-drilled to be physically self contacting.
Other than that, a very very good product.