First off, that book is from 2017, and while I might not be an expert, it doesn't seem like easy content, but that's not the problem. Maybe because the original English lecture was AI-dubbed into Korean, there's a problem with it being slightly awkward, and having compared a few things, I found that some are not used much now or have been replaced by much more upgraded versions, but it seems like it's explaining based on that old version. All the course reviews are 5 stars, I'm not sure what kind of people they are, but it seems I was properly hooked by Inflearn's marketing. I bought two and immediately refunded one. It's not like there's absolutely nothing to gain, but considering the lecture quality, the AI dubbing, the fact that it's a completely outdated 2017 version, and the price, it seems like this lecture is not worth buying. I don't know how experts would see it, but please consider that I am a beginner.