The American Museum of Natural History in New York City is a huge warren that's easy to get lost in. Fortunately, it is also full of helpful staff, security guards, tour guides, and just regular staff who are almost all happy to help and share their knowledge. Explorer makes it even easier to find your way around the museum, and has directions to some of the most popular exhibits, suggested routes for self-guided tours and the all-important directions to rest rooms and food service. Unfortunately, it isn't up to date; it directed me to a restroom that is apparently closed for an extended period for rennovation. You would think that it would at least be accurate as of the date of its release.
It is extremely useful for the casual visitor, but for anything other than highlights you fortunately still have that helpful and friendly staff to direct you. Explorer knows about a few dozen of the museum's most popular displays; my live tour guide said that the museum has 32 million artifacts in its collections, although only a small percentage are on display. But even that small percentage must be in the tens of thousands, and when we recently took a (free) tour our guide showed us many more exhibits than are covered in Explorer , and gave us more information on the items shown.
So, if you plan to visit the museum get Explorer, but also take a tour with a live docent.