The Thunderbird library is an interoperability library that prioritizes gas efficiency and speed. It uses the app-sanctioned validator model and its security relies on the independence of oracle and relayer, i.e. that they do not collude. It is also the simplest library to use.
The Thunderbird library is magnitudes more gas-efficient than many existing messaging protocols. Its gas efficiency can be attributed to lightweight protocol design and ruthless optimization.
As mentioned earlier, the Thunderbird library has the security model and guarantees as that of an app-sanctioned validator system with independent oracle and relayers. The library prioritizes gas efficiency and speed, and it excels at this very well when compared with existing protocols with the same security guarantees.