I took ortho cert exam today and passed. I wanted to share my experience for those considering/preparing it. I studied on and off for about 2 months and I used mometrix ($43.99). I have to say it was helpful but it only had 50 questions in it so I purchased this kindle
edition 550 self-assessment questions and explanations by StatPearls and it was pretty good. There were some repeating questions, but the price was great ($9.95) so I can't complain. The exam itself is already expensive ($405) so I didn't want to spend so much money on buying review books.
I consider myself a slow test-taker but I finished the exam in 2 hours. There are 150 questions but only 135 questions are scored. Unlike NCLEX, you can go back to previous questions and change your answers, but remember to just go with your first choice!