For starters the return key are different widths, which is a deal breaker if you’re a touchtyper used to wider return keys.
Programming also uses tilde and other symbols that are different between the two.
Overall they’re similar for typing alphabets, but symbols and enter key are different.
So probably he hits what on my keyboard is "ù" when he wants to enter.
I own a laptop with a USA keyboard and I dislike that, because no amount of mapping can change the fact that USA layout has 1 key less.
Dell has a few models with keyboards that accept both layouts, but in most laptops the "grid" above the keys prevents switching between them, which makes it really annoying if you ever buy one with an ISO layout, hoping to be able to just buy an ANSI keyboard later to replace it...
Order them from the Netherlands, Romania or other EU countries that use the US-INT layout.