I only see mention of the +40% to potion effects from the Alchemy specific trinkets in this post.
I think it is important to consider these trinkets for their stat bonuses as well:
Indestructible Alchemist's Stone
Mercurial Alchemist Stone
Mighty Alchemist's Stone
With reference directly to the tanking trinket i think that at this time for a feral tank the Alchemy trinket is the 2nd best in game (behind
Defenders Code). In My opinion the two will compliment each other perfectly. Both providing a different type of "in case of emergency" usage.
I base this statement on a gear comparison spreadsheet i have made using Emmerald's old weighting values (modified to account for the new values of Agility/Dodge & Agi/Crit conversions, and factoring in the increased value of Armor due to the Feral item armor nerfs).
Also there are two other things that make this trinket great:
1) Its availiable pre-raiding, and as a result can be used from the first raid onwards, unlike Defenders Code that drops within Naxx-25. Prior to Defenders Code i will be using
Offering of Sacrifice which is from a heroic.
2) It is only a rare item, and it will be fair to assume that Blizzard will add an epic version to the game that will be availiable through some sort of rep grind like with the Shattered sun offensive items in TBC, or through the daily quest tokens.