I've used guides for other games (the Final Fantasy series in particular) to be sure that I've completed all of the side quests, know which weapons have better stats and where to find them, etc., and I wish I had paid attention to the reviews of this guide before I purchased it. I read them while it was in transit, but figured it was only $14 so no harm done if it wasn't quite up to snuff. It's significantly below par.
Between talking to your crew between missions, your yeoman giving you a heads up to keep you from forgetting a loyalty quest, the linear nature of the missions and the blue highlighting on the screen when you point the reticule anywhere near a wall safe or other searchable object, you really don't need the walkthrough.
Areas where a walkthrough would be helpful would include better combat tips for difficult fights, including pros and cons of various heavy weapon choices going into a section. However, there is remarkably little along these lines that is useful.
The writer also makes no effort to consolidate upgrade information in a useful way. They tell you what the upgrades do, but not where each of the five damage upgrades for a weapon can be purchased or found. This would have been really useful information if you wanted to focus on getting all of the upgrades for a particular weapon type first, or find all of the damage reduction upgrades as early as possible.
The planet information is displayed in such a horrible table, I would only consider using it to locate planets with Element Zero resources, since as long as you mine the other planets as you need resources, you can generally keep up with research.
All in all, I would *highly* recommend waiting until something gets put together on GameFAQs or other online resource, as it's bound to be much more useful to you. As someone else noted, the maps can be handy... but again, the missions are so linear it's difficult to miss anything unless you're breezing through. The one exception to being easy to find that I've found was the pistol upgrade in the assassin loyalty mission - for which there is no map and the reference is buried in otherwise useless text.
Spend your money elsewhere.