I personally like the buff. it probably wont make me go for mastery contra haste.
the reason i like it is that my gear will have mastery, either i want it or not. only end game will i be able to choose it away(not trough reforging but trough selective gear). so until then the mastery i do get is not just a wasted stat, it actually does something to my damage.
i havent run the numbers, but i expect that this will give a minor increase to your damage wether you are just beginning at lv 80 or are in the late late game.
what really disturbs me is that crit is at a such low dps per point. i really think that crit should be better, and it may be in the later game. hopefully