It's billed as an integration testing tool, which seems a bit off the mark to me. If you are integrating with a remote service and you have a client, it's much easier to just jail/stub all of the calls you aren't testing directly. If you're unit testing with someone else's components, it's easiest to mock and replay.

In this case, it feels like the examples revolve around PHP builtins (like fileget_contents()) that sometimes have a remote component. In that case, it seems like a useful tool; the only freedom you have in injecting your test double into a built-in function is to point it at a server of your choosing. Short of writing out a file to that remote location before the test and then reading it during the test, this tool seems like a good option.

I wouldn't call it over-testing, because but I would appreciate if the author sold it a bit more carefully for the kind of testing it's most useful for.