One could argue that you don't need a sourcebook for Star Trek as you can just look online at Memory Alpha wiki, I would disagree as this book provides a lot of detail. It provides a wealth of background info on the Klingons and Romulans, as well as the stats for their ships. It also gives a good deal of info on the Gorn and the Orions, who both make excellent antagonists for an adventure and tend to have been forgotten by more recent Trek incarnations.
It's a good solid lore book that also backs that up with the stats for the races and ships of the quadrant (Benzites & Bolians and a bunch more are added to the PC races)
Overall it's a solid addition - but you might get more from one of the division source books first. That saying if you're all in on the books it won't let you down.