It performs well enough on my connection, because it's pretty good about playing "load as you go." But it's loading a lot of stuff. By the time I scrolled to the end and read through the entire timeline, this "web page" had loaded over 52M of data.
Speaking of scrolling, I had to scroll both down and to the side at various points to accomodate that "clever" timeline thing. I don't think this sort of approach is particularly user-friendly. It's even worse on mobile.
Mobile! As noted, this site doesn't do well on mobile, and it's not doing badly on mobile in a "Well, all sites are bad on mobile, [shrug emoji]" fashion. It's very clear that the site is trying to demonstrate responsive design: it's not "broken because tiny screen," it's "unpleasant experience because poor design choices." Former Congressman Henry A. Waxman is a lovely fellow, but I don't actually need his image in a partially-transparent overlay taking up nearly half the screen of my iPhone XR when I'm reading his forward. The timeline display is even more annoying on the phone, as it starts with a non-modal "swipe to navigate, OK?" demand. If you get past that, scrolling gets janky, until you move past and get another fixed image which only takes up a third of your screen this time. So yay.
Actually, I'd argue scrolling is kind of janky even on the desktop, in no small part because it's doing all this fancy "here's a picture scrolling up with the text! now it's fixed! now it's scrolling!" Is it pretty? I guess. Would it be less pretty if the images were just, you know, images on the side of the text? Not really, and if you just let a web browser scroll a page without this kind of fluffery, it scrolls really well! Scrolling turns out to be a solved problem! Also, does the picture of Former Congressman Henry A. Waxman need to be that big on the desktop? No. No, Mr. Waxman, it does not.
Last but not least: you know how I mentioned the web page was over 52M of data? The PDF with the same data is only a hair over 36M. It doesn't have a cute scrolling timeline in it, but it does have footnotes. Which the Shorthand web version doesn't. The web version has footnote numbers, but they don't go anywhere -- no links, no popovers.. For a report that has 61 footnotes, this is actually a pretty big fail.
So that's my issue with Shorthand. Thanks for asking!