Completely unaffiliated with any of the parties involved but recently familiar with both Heap and Segment: Segment (and presumably this solution) is more like

Completely unaffiliated with any of the parties involved but recently familiar with both Heap and Segment: Segment (and presumably this solution) is more like an event mux/demux. All your disparate event sources connect in, and you send the data to places like Heap to visualize it. Segment's value is acting as a central, common location for your event data. Heap's primary value is visualization/analysis for things like retention/etc. You can collect data directly through Heap as well but I wouldn't say that's the primary value of it.