I have followed the link and the download is free.
Quote from the FAQ's
Is this really free?
Absolutely. We want you to experience Audible the way a full, paying member would, so we are offering you one free month. If you like it, you are invited to stay on as a member, paying as little as £9.49 a month, STARTING with your 2nd month. There is no commitment and you can cancel at any time.