OnOff SHIM observation/question

Am I right in thinking that to shutdown you have to press and hold the button and to switch on you have to press and release to button?

This is correct- the press-and-hold to shutdown is to prevent an accidental press from issuing a shutdown. When it’s off, there’s no software involved and it’s just triggering a latching circuit.

It might be worth mentioning that on the product page (the first time I tried to shutdown I thought the shim wasn’t working !)

Agreed, and done! Thank you.