Author here: Yes, there are certain functions where writing good tests will be difficult for an LLM, but in my experience I've found that the majority of functions that I write don't need anything out of the ordinary and are relatively straightforward.

Using LLMs allows us to have much higher coverage than if we didn't use it. To me and our engineering team, this is a pretty good thing because in the time prioritization matrix, if I can get a higher quality code base with higher test coverage with minimal extra work, I will definitely take it (and in fact it's something I encourage our engineering teams to do).

Most of the base tests that we use were created originally by some of our best engineers. The patterns they developed are used throughout our code base and LLMs can take these and make our code very consistent, which I also view as a plus.

re: Complacency: We actually haven't found this to be the case. In fact, we've seen more tests being written with this method. Just think about how much easier it is to review a PR and make edits vs write a PR. You can actually spend your time enforcing higher quality tests because you don't have to do most of the boilerplate for writing a test.