The extension isn't storing any data from Zillow. Bigger Pocket's proprietary calculator pulls the data from Zillow as well. I think as long as you aren't storing or trying to make it proprietary it is better.
I installed the extension but when I click on it (in Zillow) all I see is an EMPTY popout panel ...
Hey, interesting. Make sure you have a home opened and it should populate with the charts. If that doesn't work feel free to send me an email at caleb at homescope.io and I can help you out :)