If you still have doubts, here are two simple ways to reduce risks when using it:
- Create a separate browser profile or use a different browser exclusively for working with betting sites and the extension.
- Enable the extension only when you need to load betting history, and keep it disabled at all other times.
I still think doing these carries a huge risk. For example, there might be an exploit where an extension accesses a profile browsing data history in the background, or they do that whenever they get activated, so there's no need to monitor everything. It doesn't help that news about an exploit or a new zero-day bug that allows someone to abuse a browser function keeps being reported. I believe going open source or at least making a basic version that everyone can verify is the right move.