Other posters have given you various pros & cons (so apols if I repeat some of them).
Mainland EU universities don't operate in the same way as UK ones. Very little emphasis on the 'student experience' and most students live at home, or commute, or flat-share with friends. This may make it very difficult for someone who doesn't speak the language or without close connections to a country or an area.
No student loan for tuition fees or maintenance.
Often very big classes, and very little personal attention - teaching through lecture only - certainly that's the 1st hand experience of family members in the larger better known French, German & Italian universities. It generally takes a lot longer to complete a degree in these countries, and degrees are usually a minimum of 4 years.
So they may teach in English in the Nederlands, but everyday life is conducted in Dutch.
HE in the UK (against all the current odds of governments trying to destroy us as they are destroying State schools) is world-leading. Your DS can choose the best Physics degree, rather than the one taught in English in another country. The fees are quite low in international terms, and don't cover the actual cost.
Is your DS thinking of staying in Ireland or the Nederlands? He'll make friends & develop networks in these countries - will such networks help if he decides to return to the UK? Or is he interested and committed to spending a good part of his career outside the UK?
A degree isn't just a commodity which is interchangeable in country or language.
And I suspect it's a false economy to look just at the debt of the loans. Think of the debt instead as enabling an investment, and the best investment anyone can make in themselves & their long future life.