I believe many new ICU nurses want that CCRN for the wrong reasons. Cramming to 'pass a test' is no way to demonstrate critical care expertise. This comes with time and experience. This is not nursing school anymore.
My advice is take a critical care internship and work ICU for several years and soak up all the knowledge and insights you can. Attend all the critical care seminars you can...network with other critical care nurses....enjoy your job. THEN you will be ready to attempt the CCRN ...and WITHOUT taking a 'course' to pass it.
If one needs a good review I agree Laura Gasparis Vonfrolio's critical care 'pearls' systems review is the best.