I purchased Harrisons (got it really cheap on ebay) but only did a couple of chapters while studying for the step. The questions were much more detailed and "trickier" than the questions from q-bank and NMS and the ones on the actual test. If you are desperate for more questions, use it but start with the other sources first.
FWIW...I've done about 80-90% of Harrisons. It was excellent for the IM NBME. I dunno how it will help for Step 2 (i haven't taken it yet). But it seems a bit more detailed than necessary.