This add-on claims to have "offline" voices which are "never sent to the internet".

However if you block access to the servers it contacts using a firewall:

1) You can see tons of access sent to "support.readaloud.app" and "chart.googleapis.com"

2) The text to speech stops working entirely. It won't read at all and says "Phone not connected". You can't even use the example offline test voice in configurations panel.

How is this even remotely offline if it can't work when not connected to the internet and their servers in particular?