"Deadly Toxins: Poisons" serves three overlapping yet distinct audiences equally well: DMs and players who don't know much about poisons to begin with, DMs who want to use poisons in their games to challenge the PCs, and players who want their PCs to use poisons. All three audiences will find plenty of useful information and ideas here.
The crunchy parts of the book provide D&D 4e stats, but there is plenty of system-agnostic information here, giving the product broad applicability. In D&D 4e terms, most of the rules are judiciously written, though some elements are highly questionable. The warlord utility power "cleansing wind," for example, strikes me as thoroughly magical. I can understand the warlord's core "inspiring word" power as nonmagical, since I've seen "Rocky" and plenty of other sports films, but I can't really convince myself that a warlord could use martial skills to push poison vapors away from herself and her allies. However, this is a relatively minor complaint when stacked up against the extensive list of real-world poisons and antidotes expressed in game terms.
Better writing (in terms of English grammar and style) and/or editing could have improved this product significantly. From awkward phrasing to misused words ("run the gambit" instead of "run the gamut," for example), page after page annoys attentive readers. When you buy a PDF gaming supplement, you're essentially buying words, and it's reasonable to expect proper, even skillful, use of those words.
In sum, I cannot honestly say that this is the best 4e supplement detailing poisons, and it's not the one I would choose to use in my campaign. But it's not bad at all.