ahrens is a smart dude--he works here in saint louis at washington university
i studied his books back in the 90s--riddled with errors, but concise.
i wouldnt gauge your chance of success on his product.
the test is difficult from what i have been told. personally, i would purchase every question-bank book on the market (even the old stuff-gasparsis has one) and understand all the questions. i would included ccrn, pccn, cen, and cfrn (minus the flight physiology) information.
it is more than just the information that is presented in seminars. i mean, yes, i would probably subsribe to meded and watch their ccrn, pccn and next product (72hrs of videos), and i would buy gasparsis' dvd product (i just did, along with hemodynamics--need to figure out how to resell), and i would watch these videos a few times over.
but a bank of 5,000 test questions wherein u understand the rationales, etc, provides for a well-rounded 'trauma' background that would serve u beyond the exam itself, in addition to feeling secure about testing for the certification
just my 2cents
but realize i over-do my studying as a rule