I've used all the free (or almost free) datascan programs I could get my hands on. This program is one of the best as far as the inexpensive ones go. It has tons of features and works great. It's not free like some others have mentioned, it's $20.
The free Conzult program is ok, but it's very limited in what it can do. Nissan Data Scan is definitely much better. The full Conzult program does look better than Nissan Data Scan, but it's $150 compared to $20.