You may be correct.  However, the book can be shown to the deaf person, and  if necessary that person could point to their needs.  This is, of course, excepting very young persons, who will not always be able to answer any questions to the satisfaction of a non-signer or a sign language expert.  I believe the idea of Paul's original question was to find an interim means to help communicate, not to solve every issue.  And you must admit that if you can get someone into this series of little instruction books, that person will gain more knowledge of ASL movement than not.  Yes, it appears to follow signed English grammar.  However, again, you are working with beginners (adult age fireman) who just may not understand ASL's way of talking, otherwise.
Just my thoughts on the matter.

Jerry
mailto:jzs@xmission.com