Some years ago, I did study Bahasa Indonesia with a couple of hard copy text books from reputable sources, and had a 1x/week in-person tutor. I did learn some of it, and could speak a little when I visited. But six months ago, I found an online tutor who recommended this book, but did not buy it for the 1st month. The price is very reasonable, and has made a HUGE difference in my ability to study and review. It allows exponential progress! I still work with the tutor 2x/week, and also have review study sessions with another of her students 1x/week. That student had worked with her for over a year, and had not purchased the book. I told her that it is a remarkable tool. She now agrees! For those sessions, we just go to the same lesson in the online book, and use our phones as we discuss and complete the lessons.
If you want to learn Bahasa Indonesia, The Indonesian Way is an essential best tool. The interactive exercises and cultural explanations are remarkable…way more than I had expected.