I only used CFAI materials and passed the first time round. I would say that (1) if you start early (i.e., now), (2) if you are used to taking exam (i.e., you can determine what’s core, what’s secondary, and what’s not-very-important - even if it is sometimes tricky, but at least you have a pretty acurate track record in this area), (3) if you are disciplined (i.e., you establish a schedule and stick to it) and (4) if you have a minimum level of familiarity with most of the topics covered (in particular derivative instruments and portfolio management), then I think that CFAI materials are good enough. However, if you cannot tick one or several of these conditions, then go with Schweser or Stalla. They will definitely save you time, focus your attention, and minimize (though not eliminate) the risk that you need to come back the following year.