ESXi 5.5 has dozens of unpatched security flaws. Running it in a production environment or exposing it to the internet is extremely dangerous, regardless of how you license it.
While finding valid, high-quality license keys on GitHub can be hit-or-miss due to GitHub's Terms of Service esxi 55 license key github hot
Shared keys may stop working, reverting your host to evaluation mode, which expires after 60 days, potentially bringing down virtual machines. ESXi 5
: Leo pasted the key. The red "Evaluation Expired" warning blinked once, twice, and then... vanished. reverting your host to evaluation mode