Generally Dutch universities offer good quality education, and many will be roughly similar in terms of quality of education. In that sense, you can't really go wrong, but if your son has Oxbridge potential, then he might be better off going there.
While Dutch universities offer a lot of courses in English, it is important to remember that many of the staff are not native English speakers. While some (many?) will be used to conducting research in English, collaborating with international colleagues and might have been teaching courses in English for a number of years, others will simply have been told by management that the course they have been teaching for the last twenty years now needs to be taught in English. Your son will need to be prepared to possibly be taught by people whose English is not perfect, and to be surrounded primarily by students for whom English is a second language. Some of this will be different again if he is planning on studying for a Liberal Arts & Sciences degree, which has a different set up from most university courses.
Apart from that, will the university offer accommodation to first year students? Many universities do not, and finding housing in the Netherlands (especially Amsterdam) can be difficult for Dutch students, let alone for international ones who don't know the housing market. If your son has to find his own place to live, then make sure he becomes aware of the local rules and regulations, Dutch regulation tends to be stricter than in the UK, for example around how much rent landlords are allowed to charge.
This all sounds a bit negative, but I can highly recommend doing a degree abroad. I moved from the Netherlands to the UK to study (because I wanted a change of scenery rather than for any concern with the Dutch education system), and I believe it does help young people stand on their own two feet, learn new life skills, and become independent even more so than if they move within the UK to go to university.