Should I take a Certificate for University Teaching while doing a postdoc?
I would recommend you to take the certificate now. The reasons are the following:


Although research excellence still remain to be the most important criteria for early-career faculty members, it is rarely a single criteria candidates are compared on. In the UK it is increasingly common that new faculty members are expected to teach from their first day in the Division; an evidenced skill and knowledge of the process can give you an advantage over other candidates, excellent in research and research only. I don't know what is the situation in other countries, but I have a gut feeling that academia across the globe is becoming more dependent on student fees, and hence the emphasis on teaching skills will increase.
You seem to do really well on research front now, having your own fellowship funds, etc. You are clearly appreciated and valued in your current Division. However, you will need to establish yourself in the new place in the new role of young but fully capable faculty member. This could include a lot of teaching, plus a lot of administrative work you're not familiar with now. Transition from research-only postdoc to a faculty is not a smooth one. It is quite important to be prepared to the faculty role as much as you can, before you take it. So, it is worth spending 200 hours now rather than later on top of other commitments.
It is not uncommon for people to move between countries and departments and having their certificates recognised. Commonly, HRs would need some evidence, but as soon as they can read the document, they are likely to accept it.