The latex topper is like a thinner version of the seatbone saver. It is suede covered and filled with latex which is always soft even when cold and so useful on the saddles in cold climates when they might otherwise feel hard to the rider's seat for the first few minutes of riding.
Of course, they also look stunning, and are a good way of giving a suede seat on a leather seated saddle (also they have the little badge on the back to make your saddle look like a Vogue

) They are specially fitted for each model of saddle (SBS, Fhoenix and Vogue). I have a little picture of one on a saddle

Fiona