The two major issues holding us back from making it the default are really the performance (still not good enough) and some adjustments needed in the Yul->EVM transform (i.e. you can still run into “Stack Too Deep” in some corner cases).
Has this been tested out or are there ways to test it? Is it secure for deploying a smart contract to mainnet?
There are no unresolved security issues. It has been thoroughly tested and we consider it on par with the legacy pipeline in this regard.