[stephengillie]

I took it to mean "instead of buying, try it out."

After hearing the part about the "perceived desirability of the user", I'm thinking maybe they only want to sell to certain people today, perhaps return visitors? Maybe they want all their new visitors to try it out before buying? They could have the button change based on cookies, and they just started an ad campaign that's on HN's front page.

Edit: This comment was unhelpful? If not, why downvote?

[davidjgraph]

Possibly, or given the source to whole thing is on github, you could just look at the HTML of the page there, https://github.com/jgraph/draw.io/blob/master/war/about.html