I really don't see
[Shard of Woe] as being something fire mage should consider, as there are definitely superior options available this tier, such as
[Theralion's Mirror] and
[Bell of Enraging Resonance].
Taking a look at
[Shard of Woe] specifically, let's breakdown both bonuses that it provides:
[1] Reduces the base mana cost of your spells by 405. So essentially what we're looking at here is netting X amount of extra fireballs over the course of the fight without having to scorch in between. I doubt the value of this for a couple reasons:
a) In full 346 gear with a few 359 pieces, I find myself with zero mana issues outside of fights where I need to lay down heavy AoE damage, and even in those cases I don't find myself hard ooming. The fights that currently exist where you can realistically turret and spam fireball are few and far between, even without consciously weaving Scorch into your rotation you'll be doing it on the move in almost every fight this tier.
b) We won't be able to make any real conclusions on this until someone obtains it and tests it out, but as others have mentioned previously, this may cancel itself out partially by reducing the amount of mana returned via Master of Elements, further reducing the value of the mana cost reduction. And by the time one would obtain this trinket, their crit would be at a fairly good level in mostly 372 gear.
[2] 1935 Haste Rating for 10sec, On Use, 1min CD. While a 1min cooldown on a trinket use is nice, 10 seconds is not a very long duration, and, well, it's haste. The most obvious uses for this would be combining it with Combustion for extra ticks, or even Pyroblast! / Living Bomb if your natural haste rating through gear + the use effect would give you an extra tick. So while it's not terrible, I don't think it compares to the effects of other trinkets available this tier (Bell of Enraging Resonance has a spellpower proc and Therlaion's Mirror has a Mastery proc).
[Theralion's Mirror] likely being a no-brainer for trinket 1 because it's currently the only raid trinket with INT on it means
[Shard of Woe] competes for trinket 2, and I think
[Bell of Enraging Resonance] is just plain better.