Security of open source Android on SONY Xperia smartphone

I really am quite taken by Sony’s Xperia series smartphones, but I don’t like Android, given how it’s parent company makes it’s money.

Sony offer the opportunity to install the open source version that they use for the smartphone and I would like to know the security implications of that. I don’t expect it to be audited, and I am not going to sift through all of the code myself, but it’s removed a hurdle for me and now I don’t know what to do ?

ref : https://developer.sony.com/develop/open-devices/get-started/supported-devices-and-functionality/

Yes I like open source, as it is harder to hide malicious code, but how to check for it ?