In my experience this is basically a turnkey setup with Tinc though as it handles all the key sharing transparently, and in your example will only use computer

In my experience this is basically a turnkey setup with Tinc though as it handles all the key sharing transparently, and in your example will only use computer b to do the initial handshake and then let computer a talk directly to computer c. This is especially useful when you have large mesh networks across various LANs and WAN.