I use the QC35 every day and it can do ANC without anything playing as well, in fact it is impossible to have the power on without ANC active, just like the QC3

I use the QC35 every day and it can do ANC without anything playing as well, in fact it is impossible to have the power on without ANC active, just like the QC35 II. IIRC the only difference between the I and the II is the Google assistant button. There's a marked but subtle difference between having the headphones on and off, which can be confirmed by having the headphones on and turning the power on and off without removing them. The difference is not huge, and the headphones will block noise much better if you play music or white noise to cover up ambient noise. The headphones take forever to power up and down because of the voice prompts, and this will be faster if you turn off voice prompts and use beep mode instead. The comparison is easier this way.