I might be posting this a bit late but my review of the DevOps Professional practice exams is based on the exams i have taken in November and December 2017. I have given the actual exam on December 23rd 2017 and passed it with 77%.
My preparation for DevOps Pro exam was done using a pluralsight course by Mike Pfeiffer. I have detailed out the preparation and approach i have used for this exam in this linkedin post.
Questions: I waited for whizlabs to launch their practice exams for this exam but after some delay i think they launched this in September or October of 2017. The practice exam questions during my initial stages of preparation seemed tough as the course i used to prepare did not have any practice questions and i only passed SysOps Admin and CSAA before this. But as i learnt more about the topics in DevOps pro i passed my second practice exam with a higher percentage and there on i felt the next three had a bit of overlap and i passed the others with a higher percentage. After taking the actual exam i felt the difficulty level of the questions should be much higher. I am not sure if whizlabs have updated their current version though. My advice to test takers would be to know the concepts in and out and use the exams to prepare a strategy for time management. If you eliminate the incorrect answers and if you understand the question correctly that helps you to pass the exam.
Reasoning: The reasoning or explanation they provided for the answers is pretty good. I always looked at the reasoning before moving to give the next exam. I felt some of the reasoning was not correct for some questions but it was easy to reach out to whizlabs experts and sort it out. Since this exam scope is limited to some services of AWS i would advice to read the user documentation first before using any course or exam.
Overall, I think the practice exams did help me to boost my confidence and prepared me to what to expect in the actual exam. So i think it is not a bad investment considering they are cheaper than the AWS practice exams and you have the option to pause and retake your exams whenever you want. Also, whizlabs experts responded to any questions I had.
P.S: The AWS practice exams that i have given from AWS or PSI site were terribly phrased and i actually did not pass them but i still went ahead and scheduled my exam as i was confident of my preparation. All the best!!