It's Edward Eager, so it's worth reading, sure, but it's one of his lesser ones. The magic system is sort of random and unconvincing (as opposed to Half Magic, so specifically and originally delineated), the characters are (with the exception of a little-seen elderly guardian) barely drawn, the adventures are unexciting, and it simply pales in comparison.
Oh, and it's awfully of its times, in both senses of the word 'awfully,' including an Indian attack against American colonists, and cannibals on a South Seas Island. For a moment I got excited because the author introduced escaping slaves, but they didn't exist as characters, only as opportunities to show how nice and helpful the white folks could be.
So while it's pleasant enough, perhaps it's one of those books by an otherwise classic author that are better left unread, unless you're a completist. Certainly don't start here!
P.S. N. M. Bodecker's illustrations are always wonderful. He's up there in my top 10 of children's book illustrators. If he's involved, it's hard for me to say no to a book!
(Note: 5 stars = amazing, wonderful, 4 = very good book, 3 = decent read, 2 = disappointing, 1 = awful, just awful.)