seal or not seal?

We have a granite countertop called Black Impala.  I was not aware that black "granite" might not be actual granite at all.  The installer sold me a sealer called Stonetech Professional and recommended that it be applied every 6-12 months.  Is this a stone that should be sealed or not?  Also, several months after the countertops were installed, we noticed rings that were left from a bottle of Sangria.  Any recommendations as to how to remove these?  Thank you!  Patty