The historical context is appreciated, but I would recommend marking it as extra information. Many textbooks move extra content into boxes offset to the side of the page. Perhaps something similar could be done here. (The same goes for the cultural facts)
I like that the book explicitly states that it is essential to remember to include the tones when writing pinyin.
It's pretty smart to add a new diacritic for the half third tone, which I am guessing is borrowed from Vietnamese. The note that there are different signs for counting is also a practical mnemonic device. I like it a lot.
Overall, while I already knew some theory, I managed to learn a fair bit.
By making me recite just two tones at a time at first it taught me fairly well, though I still have huge trouble speaking fast.
The pinyin has been a bit too helpful in this exercise. Not that sure if it should already be there unless that's the intent.
I am frankly kinda tone-deaf, so I often rely on pitch length and creakiness to differentiate between tones.
I appreciate being reminded to learn the tone numbers, as I had not bothered to do so previously and only called them by their contour.
Reciting the exercise was actually quite fun. The fact that it's mostly just the first and second tone helps in remembering it.
I couldn't remember it, but reciting it was fairly enjoyable.
Pouze iniciálu H z této skupiny naopak oproti češtině budeme vyslovovat zněle.
Is this trying to say that we should say /ɣ/? I'm a bit confused here.
I would prefer going into more detail explaining [pʰ] in Germanic languages. I often try to explain it to people as the difference between the Czech and English word-initial p in "park."
It might be a good idea to note that some Chinese languages maintain a voiced-voiceless distinction. The book should probably explain what "ü" sounds like before it's used in text, even if most people understand what it means.
I will be skipping comments for most tonal exercises as they are repetitive and there are not many unique comments that can be given.
I made one mistake. "Lēi" confused me.
I'm not sure what the point is of having just two tone types. Perhaps the exercise should be explicitly labeled as "tell the difference between these two tones" instead of an exercise for marking/counting tones.
It might be a good idea to explain the two-vowel analysis, although it might clash with the pinyin being taught. The book should note that "uo" is written "o" in certain cases, rather than introducing it as a separate vowel sequence. This is already explained with "ü."
"Iong" [yuŋ] should be [juŋ] I believe. The book does not actually explain erization ( /ɚ/) despite refering to it several times.
The symbols /ɿ/ and /ʅ/ are non-standard (I only know them because I was looking through obsolete IPA symbols). It might be better to denote them as /ɹ̩/ and /ɻ̩/, or at least note what the standard notation is.
Writing "lǜqì" was really confusing for me since I'm not that used to stacking accents like Vietnamese. It might be a good idea to note that this is even possible, as I had to double-check to be sure.
(There are too many exercises here, I haven't done most of them)