This is really clever, but I found a couple of limitations:

(1) It seems to be based only on total distance, not weighted in any way for example with regard to transportation routes or methods. So for example, people coming from San Francisco and Berkeley are encouraged to meet on Treasure Island. This could work if they're both driving and they put a very high priority of having each person drive a very closely comparable total distance, but is otherwise probably inconvenient.

(2) Similarly, it's so strict that if the geographic midpoint between the people is over water, or something, it will just give up and return no results.

I don't think those behaviors are a very typical human-like way of thinking about the problem of meeting in the middle, where other factors like traffic, public transit, parking, more meeting options, and actually being physically able to meet at all would probably have non-zero weight!

For instance, to meet in the middle between San Francisco and Berkeley, I would probably suggest Oakland rather than Treasure Island (or rather than giving up for lack of an exactly equidistant location). There are more places to meet, and also more transportation options for reaching it from both ends. But it is somewhat closer to Berkeley, so this service rules it out completely.

It would probably work great for a region that was much more homogeneous in settlement patterns and transportation options, maybe like Chicagoland?

This website breaks the back button on Chrome/desktop/windows. I had to click and hold the button to leave the site