The interface is pretty plain ... just a large text box with a counter down in the corner telling you how many words you've cranked out so far (and a thing that shows when one's scribblings have been auto-saved), and once you cross the 750 word line it pops up a notice to let you know you're done. I doubt many people just STOP there, but it's a signal that lets you wrap up your thoughts.
The thing, however, that has gotten me (and, obviously, my OCD) excited is all the DATA that it spews out once you're done. Not only does it keep track of your daily total, your cumulative total, your words-per-minute rate, etc., but it gives you all sorts of analysis as well ... from a "rating" (like movies) to what you're "Feeling mostly ..." (so far I'm 4/4 on "upset") and "Concerned mostly about ...", with pie charts breaking down what can be quite a few elements, to a section on "Mindset while writing ..." which breaks down (with pie charts) dualities of introvert/extrovert, positive/negative, uncertain/(certain?), and feeling/thinking. It also analyses what you wrote for "time orientation", "primary sense", and "us and them" (pronouns used, I guess). One section that I didn't include in the graphics here is "frequently used words" (since you can sort of re-create the themes of the piece by looking at those - and I've been really letting the Shadow out in these so far).
Anyway ... if you click on those you'll get a full-sized version to check out ... fascinating stuff!
I've seen things saying that this is "as good as meditation", if used this way, but in Handley's book the "750 word" exercise is presented as an "exercise" for building up your writing chops. Since I'm averaging right about 20 minutes for my 750 words, I think I'm in pretty good shape (and should probably ratchet up my expectations ... but I don't really want to burn much more time than that), at least as far as my fingers are concerned.