I like it. it's got potential. With north of 5000 pdfs in my library I'm extremely open to tools like this, and the methodology seems pretty sensible to me. But at present it feels kind of random - good at picking out summary sentences of what a document section will cover, or emphatically stated conclusions, bad at highlighting necessary context. I wonder if it might be better trained on clauses rather than full sentences, although that's probably significantly more work.
I'm sorry I don't have a more positive review, but I think it's a bold attempt even if it falls short, and want to see where it goes. Even as is, I can see myself using it sometimes as its selections offer an interesting alternative to my own skimming/emphasis preferences. Very impressed with the clean no-BS user interface and fast performance.