I did my PPL back in 2006-2007 and things seem to have changed. There's now Operational Procedures to do and Comms will have changed as well. The format and style of questioning has changed as well. There are also new concepts such as convergency in Nav and when I was flicking through a comms PPL book the other day they had stuff about TCAS and stormscopes! I saw a chapter on building a bivouac and how to collect fresh rainwater in another APM PPL book. They'll be teaching polar stereographic and transsonic flight next...
I wouldn't say buying the CDs was a bad idea just as long as you're not planning to rely on them solely to pass the exams or else you might come a cropper. Still, any resource on aviation is useful, you never know when it might save your life!