[flatulentone]

Considering that digital electric meters have been compromised, and that the one I studied had dual-band radios including WiFi spectrum, it may be best to assume that there may be unexpected data pathways that could use a MAC address. Note that the WiFi of many routers broadcasts the wired MAC addresses on the LAN as well as the wireless clients.

You're right about false-negatives with sniffers. If you read the source on pages you visit, you'll see https analytics data mining, so don't assume that every outgoing https connection is okay. (and some browsers don't use your normal DNS / hosts settings, so sites you think are blocked may not be)