I believe LinuxAcademy.com and the extra white paper suggestions as well as real-world use is enough to pass the exam. I did, however, also take the courses at acloud guru. I felt like it would give me a different perspective from a different instructor, and it also provided an entire extra review of all the materials. My study time was done over 3-4 weeks and included all the videos and labs for all three Associate tracks as well as many of the recommended white papers. I basically crawled into a hole for that month and just studied. I spent 40-60 hours/week on top of my regular job and life to get all of that covered. I learned a huge amount during that time. I was able to take many of the concepts and apply them immediately at my job.
My recommendation, especially if you do not actively work in AWS, is to take longer and really practice the concepts you are learning. When I interview people who have certifications, I specifically ask how long they studied, were there bootcamps involved and how much real-world experience they have. I do not appreciate "paper" certifications, so I hold myself to the same standard of really knowing the material. Read the AWS forums and try to contribute, study the white papers and do all the labs. This is an exciting field and can be a lot of fun.