We are using Reflect.run at Roboflow and it really is very slick. We have it testing our core flow on a schedule so we know if any of our 3rd party services or dependencies go down and/or if we introduce a regression.

Our app's core workflow involves signing in, uploading images and annotation files, parsing those files, using HTML5 canvas to render previews and thumbnails, uploading files to GCS, and kicking off several async functions and ajax requests.

That Reflect.run was able to handle all of those complex operations makes me pretty confident it can effectively test any web app.