This review applies to the 1979 edition, i.e. the reprinted 1953 edition, that I've read.
Seven decades might not seem like a lot in humanities, I would dare say it really wasn't even not as far ago as in the early 70s when studies from early 20th or even late 19th century were still quite similar when it comes to methodology, but it is, the more now since a lot of new ways of doing research appeared in the last half-a-century. Yet, I would still recommend this book as a fair base for anyone beginning to look into contact linguistics. I'm not sure how much has changed in the revised 2010 edition, I'm yet to find out once I get my hands on it, so for anyone who can get that one, I'd probably recommend that one, but even this originally 1953 edition after all the time that has passed gives a good basic purview of how the general basics work and what to expect and look out for in this particular subfield of linguistics with a magnitude of references and elaborate examples on real language contact situations, not to mention it is very much on the readable side. The only thing the reader must stay aware of is the fact that it is not a new book, so any pointing out yet unresearched areas, possible approaches etc. might and probably already have been researched, tried or made standard by now.