sorry for asking, but, it says on Qualcomm page:
"This release contains a developer preview
of the user-mode driver binaries for Qualcomm Adreno 3xx/4xx GPU on Nexus 5, Nexus 6, and Nexus 7 devices running Google Android Marshmallow. It has been tested with MRA58K factory image. This release is intended only for developers, and does not meet our customer release quality
is it really safe to flash it and not having weird/buggy driver?
4.4.2 has it before.