Karma is truly open!
Don't need authentication? Delete it! Don't need internationalization? Throw it away!
There is no vendor lock-in - starting a Karma project means getting all the source code, right into your project. There is no waiting for new features or bugfixes. There are no breaking changes you have to follow because you're too deep in.
Karma contains what most larger projects will have anyways, not more, not less. A future upgrade path simply means: check the commit history the repository and pluck what you need.
This necessarily requires a bit of a different mindset:
on the one hand, you get solid defaults and can fix any potentially arising issues yourself, right when you need it.
Which is nice! No eternal wait until that annoying bug is finally fixed. You actually can fix it yourself. Karma isn't buried in your node_modules.
But it also means: you might have to fix urgent issues yourself - Karma is just here to lay the foundation. Getting familiar with at least some of the Karma code will thus be a long-term necessity. You will want to extend or cut features. For most users, the defaults however will be perfectly fine!
Where's the catch?
Karma is built with Vercel and GitHub in mind. If you don't plan on using either of them, some additional setup work will be required - but all features are generally compatible with any other hosting & CI/CD solution.