I agree with Tuborg, The IB is a term used to encompass three different programmes: The PYP, MYP and IBDP.

If your son is in the last two years of school it is likely he will be enroled onto the IB Diploma programme and therefore won't have the option to take IGCSEs.

It is usually in years 9 & 10 that you may have to decide between IGCEs and MYP. In this case I would suggest that the pros & cons would depend on where your son is likely to apply to university. If it is he UK, and you have the choice, he may be better off taking IGCSEs. Universities in the UK make offers based primarily on the student's IGCSE / GCSE profile & their IB predicted grade at the end of year 11. Although MYP is recognised it is much less widely taught than IGCSEs and the universities are therefore much less familiar with the grading system.