I failed my HESI but from what I've heard (from many, many RNs) is that the NCLEX is actually easier than the HESI for some reason. Don't waste your time with HESI books, just go out and get yourself an NCLEX study book or I actually prefer the CD-ROMs so I can just sit here and go through the questions when I'm bored. The questions are set up very similarly. To prepare for our HESI, my school just had us do a lot of NCLEX prep questions.
I would invest in a good NCLEX review book just to have and then use it to practice for the HESI. I have Saunders (blue cover) w/ the CD. It is a great book. I use it to study for my tests as well.
The HESI is "supposed" to be a good indicator if you have gained enough knowledge to pass the NCLEX, however, most people will tell you that they've failed the HESI and passed their NCLEX w/o issue.
We take the HESI 4 times during school and why we take it is to measure the instructors to ensure they are teaching us things that are going to be on the NCLEX. We are expected to fail it the first 3 times we take it, because obviously we haven't gained enough knowledge our 1st 3 semester to pass the NCLEX. They get a little upset though if you fail it your final semester because by then you should have the knowledge. However, it's still a tool for the instructors to figure out what is left to cram into our already overfilled brains our final semester.
I find the hesi ?'s to be a lot more difficult than any nclex review books. I have a hesi book and cd. The cd is awesome to prepare you for either test. I would recommend saunders nclex review. It is awesome.