That's pretty cool! Didn't know that Flexport started out like this.

Here's another example of using a landing page to validate demand, and one where the product ended up being a very successful company: https://sumo.com/stories/80-20-business-idea-validation

I recently played around with the landing page method for an idea I had and ended up not getting much traction. That negative feedback was really useful in helping me decide whether to actually code up the app. Wrote about here, if anyone's interested: https://abiraja.com/the-landing-page-method/