From experience, mahogany is one of those woods I find has a lot of inconsistencies even within the same species.
It's also an umbrella term for a variety species of wood. Factors such as climate, humidity, etc. all influence the ring formation within trees, and therefore density. Therefore I would imagine that there are differences based on the climate where each species of mahogany was harvested.
In terms of tone, I can tell you from acoustic instruments that it appears to produce a darker sound (I hate describing a sound with something visual b.t.w). I reserve my judgment for electrics, as it is my opinion that the body wood does not impact the sound as much as the neck, bridge and electronics.
For how exotic it is... a lot of instruments have been made using mahogany. However, it is now listed under CITES, therefore it may be exotic in the future.