It depends. If you want to darken the grout some, use the enhancer. If not, then just use a normal penetrating sealer from the SAME MANUFACTURER.

I would seal the tiles and the grout. That way you don't have to worry about food splatters on the tile. I have honed marble tiles for my backsplash and my GC sealed both the tiles and the grout. It's probably easier to seal both anyway than to try to go around and just seal the grout.

We just had a backsplash installed. White subway tile with light gray grout. Should we seal it? The installer never mentioned it

Grout additive will help the grout stick better to the porcelain, make a stronger grout, increase its flexibility and help it make a truer color. As far as the texture goes on porcelain. It will be easier to clean up the grout if you apply a grout release to the tiles before grouting. Grout sealers will help keep grout clean. Grout is porous and will allow stains to penetrate, a sealer will help prevent this.