FWIW, I still use ltib (originally a Freescale open-source build environment) and it's mostly great. Fewer layers of abstraction, builds all the source modules using essentially the "linux-from-scratch" system, with .rpm intermediaries that get installed to a rootfs.

I played with Bitbake, but the learning curve seemed much worse than ltib.

Edit: s/yocto/Bitbake/