Five weeks ago I passed the Salesforce Certified Heroku Architect exam. The Trailhead content is good for basics but not enough for the scenario based exam questions. A friend who had cleared it recently recommended ITExamsTopics and I got their web version for Plat-Arch-206 Exam Questions. The browser based practice was very convenient.
I prepared with exam-style questions instead of passive reading. I focused more on Heroku Enterprise at 28% and Data at 17%, then Security at 15%, Architecting Applications at 15%, Integration at 15% and Heroku Platform at 10%. I did several rounds of practice questions, real exam questions and sample questions which made the actual exam feel familiar. If you are preparing for Plat-Arch-206, check their free demo first - their Exam Questions are very close to the real exam.