1. Doesn't work on Safari. Definitely not a great first impression.
2. Sure, let's switch to Chrome (one of the three supported platforms: Chrome, Firefox and iOS). Now all I get is a blocking modal "To read on Readup, add the Chrome extension. Add to Chrome — It's Free". Sorry, not about to install an extension for something that hasn't explained why it needs an extension, let alone demonstrate any value to me, whether it's free or not.
Stalemate.
So let me ask: how do you tell a skim from a read? How do you distinguish a complete read from scrolling down to comment section (maybe even slowly)? Reading speeds vary greatly, and there's no mind-reading web API yet.