Yesterday in 10 man TotC I got the trinket
[Vengeance of the Forsaken] and I got a chance to play with it for a bit. The trinket itself definately isn't the best you can get but there might be some people wondering if it could be an upgrade for them or for their alt.
I bound the trinket to my Stormstrike (/startattack, /use trinket, /cast stormstrike) and when I start the fight only using stormstrike will get me 4 stacks instantly. Stormstrike then earthshock basicly gets the max of 5 stacks going meaning you got around 18 seconds of 1075ap. I was really surprised it stacked so fast especially since a Deathknight on wowhead claimed his dual wield abilities only got 1 stack up.
If using the trinket gets you exactly at the expertise cap I think this trinket is not as bad as most would think. An upgrade to mirror of truth and fury of the five flights in odd minute fights (1 minute, 3 minutes, 5 minutes etc.) at least and a good alternative to +hit trinkets when your spellhit capped, especially with expertise simming high before you hit the cap. I estimate the AeP value around 341 (83*2 + 1053/6 = 341 AeP) - 415 (83*2 + 3159/13)
However if your enhancement shaman is your main and you are playing endgame content everything in Ulduar is probably a much bigger upgrade.