Avoiding taxes is sound business. If a public company failed to avoid avoidable taxes, it would have a problem with its board and shareholders. Illegally evading taxes is a crime, and I'm not aware of any criminal prosecution of Apple for tax evasion.

They paid an average of ~25% tax last year.

I'd like to know more about this since the global companies I have been involved with are all sneakily hiding profits offshore, hiding them from US and UK taxes. They can't re-patriate that money, either, so innovation has slowed. This is one reason why Trump proposed a sort of tax amnesty to get that money back on shore.

Where?

In the countries where the products were sold?

Imagine you pay income tax in your residence country, making web software for global clients. If you sell your product in another country, should you have to also pay income taxes in that country or just the VAT tax for the sale?