Do these siddurim have and changes in them from the traditional nussach? I only ask because they seem very modern and free giveaways are suspicious...
"Seem very modern?" They
are modern. That's no secret, Koren is MO, and so is OU who co-published the siddur with them. It includes the Tefillah for the Medina etc.., minhagim for Yom Yerushalayim and Yom ha'atzamos etc.
I found their "textual variants" (words here and there which they chose a slightly different nusach) on page 681 interesting. I also enjoyed reading the laws and customs section in the back.
Though I find their feeling of authenticity which they seem to rub off, to be very silly and pretentious, even strange.
#justmytake