I use the Workbook / Study Guide Volume I (covers episodes 1-26) with the "Second Edition of the Alternate Edition" textbook (ISBN 0-07-252536-3) and the Destinos video series . It supplements and expands the exercises in the textbook . The additional exercises are helpful in the learning process. For me, it is a MUST to have this Workbook / Study Guide. That being said, this Workbook / Study Guide is difficult because it requires more time, more work, more discipline, more focus, more thinking, more everything. If you don't have that extra "more," I strongly suggest that you NOT buy this Workbook / Study Guide.
If you buy the Workbook / Study Guide, you will need to separately buy a set of audio CDs or audiocassettes. You can't do the exercises in the Workbook / Study Guide without the audio CDs or audiocassettes. The additional audio CDs and audio cassettes are:
Destinos Audio Cassette Program Part 1 (episodes 1-26) - ISBN 0072504404
Destinos Audio CD Program Part 1 (episodes 1-26) ISBN 0072504382
Again, you NEED to buy the audio cassettes or the CDs to accompany the Workbook / Study Guide. Be sure to reference the ISBN numbers to make sure you purchase the right one!
I would not recommend buying a used Workbook / Study Guide. The exercise answers and self-tests will have been completed - right or wrong - and that's not helpful to you.