Does this experience count for anything if you want to switch to a law firm later on?

No

Only academically. Good if wanna pursue LLM

Yes, especially if you wish to join Disputes and can get your judge to write a reference.

do you know people who have switched to law firms this way?

Yes. Firms and in house both.

Yup, many seniors.

Is this really true? Majorly heard that Clerkship experience is discounted by firms.

Its only good for LLM or if you want a sabbatical

If it is a litigation law firm, I don't think you would be able to appear before this judge.

Your experience of a law clerk can vary massively depending on the judge you work for.