Painless Speaking is written for public speeches or dramas rather than improving communication skill, if you ask me. So the content itself is pretty advanced, but too advanced for non-native speakers. Certainly, you need to change the way you talk according to the person you are talking to or the situation you are in. That's a fundamental art of conversation. I must admit this book shows us that clearly. However, I'm afraid it's going to be painFUL for non-native speakers if they deal with this first. Of course, again, it is quite useful for theater plays, musicals, and speech contests to get your message across to the audience.
Therefore, for beginners it may be literally better to start with Painless English for Speakers of Other Languages. In other words, you shouldn't deal with Painless Speaking as a textbook for English conversation classes.