Before taking the NAB exam I did both. I had a book that I studied throughout my AIT and I got another book with an on-line practice test which I found very helpful. I passed the test with no problem.
The state test had a study session a week before the test which I attended. I had to travel across the state, pay for a motel, and pay for the study session. The test was over the state regulations. I studied extensively before taking the test passing with no problem.
My advice to you is to prepare as much as possible. The tests are only offered so often, you have to pay to take the test -- so you better pass the test. I'm amazed when I hear about someone taking the test and flunking. It seems to me that they are not that smart, they failed to prepare, and they are not serious about being NHAs.