Number Six is a very straight-up lemon-lime citrus, with none of the earthy, animalic base notes of the heavy hitter classics such as Eau Sauvage, Eau Imperiale and others. The closest I have to it in my collection is Guerlain Eau de Fleurs de Cedrat, but EFdC has a stronger orange component than No. 6. I must also say that 6 is incredibly short-lived, even for a citrus eau de cologne. You have to drown in it (don't bother buying the spray bottle, go for the splash) in order to achieve any effect whatsoever. This from a guy who is EXTREMELY conservative with application.
Good news - it's cheap, it's fresh, and it's safe. No odd notes, no complicated nuances.