Not that good, for certain purposes I needed to use a certain long text which was impractical, but I needed to avoid synthetic text. I used Chatgpt to select key sentences. It wasn't that good at it. The selection was kind of random. I ended up removing some of the selection and reinstating a lot manually. But in the end, just for curiosity to see if I could get an even shorter text, I gave the summarized text to chat gpt and asked it to summarize it further. It removed the set up of an important twist, but kept the punchline. It also changed a lot of text and made up a lot of anecdotes the author didn't have. The tone changed from semi-comedic to tragicomedy and a lot of wallowing and angst that just wasn't there in both the original and the reduced text.
The thing is very bad at following instructions.