I have worked as an ICT Auditor for almost ten years in a big European bank. I was already holding my CISA certification when a dear friend of mine and fellow auditor introduced me to the local IIA chapter and to the CIA qualification: I have to thank him for having suggested the Gleim books to me (which he already used for getting his CIA) and my company for having supported me.
I found in Gleim books a valuable support for preparing for the CIA exams: they are written in a very clear way, the method suggested for studying the content is very effective, and the information is organized in a rational way. For a person who is somehow “curious” and eager to learn, as an auditor always is, these books are a source not only for just passing the exam, but also as a “quick reference” manual for your work.
The tests are also an excellent support for being successful with the exams, and they contain additional “practical” examples. After understanding their content, the actual exams are not a surprise.
The test software is user friendly and very effective, enabling you to focus on those areas deserving more attention or additional insight.
To recap, Gleim material is an authoritative source for passing CIA exams at the first attempt and, even more important, is a reference for a “real life” auditor.