• There's a lot of stuff going on above the fold. Not sure where my eyes should go
• The download icon on "Buy it now" feels out of place.
• The black text on darkish green button for "Buy it now" has not enough contrast + size is too small. Maybe try light green background, or white text.
• No Safari support as far as I can tell
• On Firefox it's not immediately clear it's supported. Most extension are Chrome-only and so is the example video. I'd like to see the Firefox icon above-the-fold
• "Try it yourself on this page" button doesn't have a :hover state so doesn't feel interactive
• The video is nice, but feels slow at times and other times too fast. Maybe have multiple named segments showcasing one feature at a time.
• The 3 panes below the video have a lot of text I'm too lazy to read. The headings aren't descriptive enough to catch my attention
• Of the testimonials only Brad Frost looks familiar to me. The quotes are barely readable.
• The "as seen in" logos have weird inverted colors. Why is Y Combinator blue? Etc.
• What's a "Hero" license? Are there other licenses?
• Can I expect future updates? How actively is CSS Scan being maintained? Will it still work in a year when browsers have changed?
• A lot of the text is very small. I'd use 16px minimum.
• Many images and video are kinda blurry on my Retina screen

Many positive points too, but this is a Roast 😁