I took the CEN (Certified Emergency Nurse) and CCRN today after doing 3 "PASS CEN" exams online last night (bought the book, went to the website, used the activation code inside cover, and activated the online material). A few days ago I did a few practice exams from a CCRN app I downloaded on my Mac from the app-store. Otherwise did basically no studying. I work in a busy ED and have been a nurse for 2.5 years. Passed the exams with flying colors. If you're a decent test taker, pay attention to ABC's, know a little about cardiopulmonary parameters, have good patho knowledge, and have had ACLS, PALS, TNCC, and ENPC, you should be fine!
I also took the CCRN exam today after I finished the CEN, and for the record found the CEN to be a little bit harder, likely because of the vast breadth of material covered in the CEN (it also has 25 more questions than the CCRN), where the CCRN is a little more focused. CCRN was "softer" in content (several more touchy feely questions), and more redundant with stroke, cardio, and ABG type questions. I did equally well on both exams. Trust me, if you use your brain and are a decent test taker you will likely pass!!!! Good luck!!!