I sat for the exam and cleared it. I would say exam is fairly difficult. 60 % of questions are scenario based. This course does decent job by explaining you the services covered in exam. But it is not totally sufficient to clear exam. Along with the course you need to go through below playlist of re-invent videos.
You must know know all these extremely well – KMS, cloud watch, cloud trail, inspector, SSM, Cloudwatch Logs, read policies the JSON format and how permissions are applied, IAM, AD federations
To go deeper read at least these white papers from AWS
AWS Best Practices for DDoS Resiliency
Secure Content Delivery with Amazon CloudFront
AWS Key Management Service Best Practices
Amazon Web Services: Overview of Security Processes
Security at Scale: Logging in AWS
Encrypting Data at Rest
I did use Whizlabs 3 days before going to exam. The questions in Whizlabs can help you to evaluate your understanding of the concepts but, real questions in exam are different and little difficult than ones in whizlabs. So its up to you if 39$ spent on whizlabs is worth or not.