From an edit to the article: "We have had a few queries as to our logging policies. We only log the time you connect and disconnect from our service, we do not log in any shape or form your actual internet traffic."

So, the information possibly gained by law enforcement is that "account X was connected to our proxy service at the time the crime was committed". I don't know how large their user base is, but it seems unlikely that the above is all that informative. Unless there are enough "criminal events" to knock the total "set of users connected during all events" down to a manageable size.