I did not use any preparation type sites/guides for sale. Some people on my board did use them. However strangely enough the ones that said they had, did not get through in the end. All of the information on that link is available freely I am sure between this and other sites (such as the student room - was a gold mine for me).
As these "products" are certainly unofficial and clearly not endorsed by OASC or the RAF I would be interested to hear their take on them.