As a 51 monk, i bought the hat. Why? because, more or less, until 70 (ohat) the mnk head slot is a total waste of a slot. Choices are: Emp pin, Fed Headgear (+1 str), or Voyager Sallet (highly difficult to obtain under anything other than extremely unlikely circumstances). AF head is a viable option, but really doesnt do a damn thing when focus is down, mnd +5 means dick in xp. So, -7 enmity on my head means the following: I can PT with ninjas. Without a thf. I can Zerk without fear of death, i can take 1st voke if i need to without having the mob back on me 10 seconds after sata.
Thats more or less a worst case scenario, but every pt has the same elements of hate control being less than perfect, as plds have yet to get af and ninjas have yet to know wtf theyre doing at all.
So to me, -7 enmity gives me a whole lot of room to punish the hell out of the mob without draining valuable MP trying to keep my bathrobe wearing ass alive. As i've discovered lately, even with the Good tanks, i can still take hate at any time with just 1 voke, 1 good 5 attk round after ws and im running for [cover]. So basically to answer your question deci, as a mnk, the hat is in the interest of mp conservation, and will hopefully affect a greater effeciency in party chaining dynamics.
ps Oh also, there will be fewer calls of "dont haste the monk". Hasted mnk makes everyone happy.