you're welcome
Not sure about the telephone shops. I actually think it really depends on the salesperson that happens to be helping you. The thing is that what you want to know is not so much how it is supposed to work (they should be able to tell you that) but how it actually works in reality. And that you usually only know when you tried it.
So share your experience after your 10 days.
I think you should just buy a vodafone sim, use it and see how far you will get.
There are also some phone shops at Schiphol airport. So if you arrive there you should be able to get the sim card there as well, I suppose.
Make sure you have enough credit to be able to activate the blox. I think the come with only 5 euro's.
BTW: I just red somewhere that the post pay KPN internet option has a FUP that is something like 215 MB. So prepaid should be the same or less. Also not really unlimited.....
Ties