It's a pretty good gauge of your knowledge in the various NCLEX categories and is a good tool to let you know what to study.
I took it without reviewing anything to get a good idea of where I stood and got a 67.8% which translated into somewhere between a 97-98% chance of passing on my first try. The faculty member that proctored the exam said that those that score 62% or higher tend to pass NCLEX on their first try.
I got 75 questions on the NCLEX and passed on the first try. I think the ATI exam helped me focus on some of my problem areas. I did awful on endocrine questions and some of the therapeutic communication quests that fell under mental health, so I focused on those areas when I reviewed for NCLEX.
I thought the NCLEX was more difficult, but that may have to do with all the anxiety that it brings. I wasn't worried about getting my RN license when I was taking the ATI. With your score, I think you have a pretty good grasp of how to test and would just review content areas that you feel you need to work on.
Best of luck to you!