CD-ROM1. NO SPOKEN KOREAN ON CD.2. CD contains a wealth of information beyond that of any other textbook. 3. Easy to navigate.4. Multi-level activities. (easy, medium and hard)5. Video and animations are clear, crisp, relatively interesting and of good quality. 6. Songs/Chants/Dances have multiple ways of learning.
I've hoarded all of the textbooks and have them on the shelves as additional resources. Keep the CDs too and switch it up. Most have similar chapters and if you don't like an activity, switch it out with photocopies.
I've been told the reason why the YBM books get chosen a lot is because they are a "good brand". There seems to be a widespread belief that because they are a large company their products are simply free of errors.