I have not read the Hillyer book, but I have used Voskamp’s and I have a very hard time indulging in her writing style. I enjoy her books like 1000 Gifts and her blog, but this geography (really more of an Earth Science) book was hard to get into and stay with and it did not engage my children like I had hoped (mine are 9, 7 next month, 5 but 7 on paper, and 4).
We did however LOVE CM’s Elementary Geography. I have the reprinted edition by Queen Homeschool. The lessons were short, interesting, provoked curiosity and discussion, and interspersed with good poetry. Also affordable and quaint.