First, it expands the 'UNIT: Defending The Earth Sourcebook' and brings it up to date without invalidating it (as Corone said). It allows players to run an up-to-date UNIT campaign, in new areas of operations and includes more details about modern UNIT. Also, it also greatly expands Torchwood 'do-it-yourself sourcebook' resources.
Secondly, it is full of new Gadgets, Traits and includes Cybernetic Upgrades.
Thirdly, the 'devices' themselves are excellent, really well-conceived and are thick with plot ideas for GM's. A single device can easily be used for a background for an entire adventure or in the case of the more enigmatic and dangerous, an entire series/campaign or even longer.
Generally speaking, as a generic resource for the Vortex System, it's a great addition. This, along with the UNIT DTE Sourcebook could easily provide resources for anything from X-Files /Fringe-style campaigns, to paranormal games (file off 'Alien' and write 'Demon').
"There are some corners of the universe which have bred the most terrible things. Things which act against everything we believe in. They must be fought." - Second Doctor