After a month of study, deploying software to AWS, and reading through Amazon Web Services white papers I decided to give the official test a shot today. I passed it on the first try. The test is much more difficult that the practice tests that I have purchased, so I recommend that you score 90% or better on the practice tests. I also recommend reading the white papers a couple of times, I really needed the details reinforced. My personal development experience was helpful, but knowing the why was helpful.
The bad news is that the AWS papers are some of the least interesting technical writing that I have had the misfortune of reading in my lifetime. Stick with it, you will be a much more efficient developer in the AWS ecosystem.
Update 2019-08-23 I even have an official badge now.