To add a bit more details, the package is 14 years old and seems more-or-less “complete” in terms of containing the functionality to map the existing sinon features into chai. So, not a lot of churn in the codebase (and the last release was a year ago). However, the last release was to add support for Chai 5 (the latest major release of Chai). So, it is at least current in that regard (and there is some hope it will be updated for future versions as well…).
Also, GitHub lists 191,000 packages as having this as a dependency so we are def not the only ones that would be using it…