Verde Cactus

We installed 'granite' countertops about a year ago. The stone is named 'Verde Cactus', which I suspect is not a true granite but a metamorphic rock, with green and pink swirls,  inclusions, and microfissures. The tops were sealed by the installer but we were advised to re-seal them after a year, which I plan to do this week. However, there is a significant coffee stain where a leak in our coffee machine went undetected for a long time. I am going to try the H2O2 poultice treatment on it today. I bought a solvent-free sealer (Magic Seal by CeramaSeal) but after reading all the excellent advice in this forum, I'm wondering if there is something else I should use. Also, how often should this stone be re-sealed? Every year? Is it known to be particularly porous?  TIA, Dave