(just in case this may help somebody)

I ended up replacing only the faulty one.
I need the car to be on the road this week, and I could not get in a hurry the cheaper ($52) Audi red R8 coils that are so "promoted" on various VW forums (fora?).
So I had to buy one from VW parts for $128.
I replaced it myself, as the VW dealer quoted $370 labour for a 15 minute job. I found one local mechanic who would do it for $130, but it is easy to do.