Thanks for your feedback!

I did have a few issues integrating Jest into a fairly mature project but this is to be expected imo for a project of this size. If you are just starting a new project, the setup should be fairly simple.

About running single tests with Karma in IDE: at least in IntelliJ, you still have to build the app and then it will run the specified tests.
For small projects, I have a similar experience as you. For larger projects, I see the greater value using Jest.