I am a fabricator.

In my experience sealer, any sealer, will not prevent stains in porous materials like marble and limestone. It is a popular misconception that sealer coats the stone and provides a barrier between the world and the stone.

In actual fact sealer protects stone by filling the pores with inert molecules. However, this "filling" process is incomplete and liquids can still penetrate the porous structure of the stone particularly if they are given time to do so. Small, tight pores like those found in most countertop materials provide on a very limited path for liquids to penetrate so sealing is generally an effective means to protect the stone.

Large pore stones like Marble, travertine, and limestone are much more problematic. Sealers made for porous stones have larger molecules of "filler" which helps but those stones, in a kitchen, are probably going to get stained and it's probably not going to take very long for it to happen. This is why we tell our customers not to use those stones in the kitchen.

There is a sealing process which applies an actual barrier like the clearcoat on automotive paint. "Hydrosheild" is one brand and there are others. It usually costs $10 - $12 per sq. ft. or more and it makes the stone appear glossier which isn't always acceptable.