Well, that statement was from someone who has lived in Cornwall for over 20 years but isn't Cornish by ancestry, so perhaps she was only going by her own biases - if she doesn't happen to know anyone who's interested in the Cornish language, that obviously means nobody is interested in it. I wasn't very impressed with her statement either, and tried to point out that there are plenty of groups promoting the Cornish language, but because she hadn't seen any of it herself, she didn't believe it. (This wasn't somebody I know personally, just a fellow member of another discussion forum I participate in.)
It's not bad! Although it's not the most exciting of textbooks, as I said before, it seems to provide a very good basis for learning the fundamentals of Kernewek. It starts in a very different place from SSiCornish - instead of "I want to", "I can", "I need", "I like", etc., this one starts with greetings and then goes on to "existence" - "Is there [something]?", "There is [something]", and so on. So it's good for expanding one's knowledge of Kernewek from what we've already learned. I will certainly persevere with it.