All substances have different densities. This is a unique property of all the elements, however some elements have very similar densities. Density is a useful way to identify an element that has a relatively larger density than another. Be careful though, metals oxidize in air and that causes their mass to increase, so when calculating the mass, ensure that you have removed all extraneous factors such as rust in order to be accurate.
I would say that density isn't the best way to identify a metal, as there is a lot of room for error, rather it is the easiest way. In my experience, using calorimetry has lead to an accurate identification of a metal.