Better than all existing options? I'm skeptical that a kernel written in C++ is likely to be better than e.g. a formally verified microkernel such as seL4. If they ever rewrite it in Rust, then it might be more interesting.
Parts of it is already in Rust and formal verification could be done for this project as well. At that stage would you be ok with it?
If it improves the security of the device and means that Google will keep updating it, then that will be good. However, personally I have given up buying Google-branded devices. They only gave me security updates for my Pixel C for three years (2016-2019).