On these outdoor countertops, we chose to spray the acid stain on them, two coats with a little time between each to allow the acid to react and create the mottling the client was asking for. After cleaning up residue from the final application (a step you can avoid with a dye stain) we sealed them.
Sealing is a critical part of the process. It can dramatically enhance the look of the acid/dye stain and reduces the possibility of the countertops being stained from stuff that gets spilled on them such as wine, lemon juice, cooking oils, etc. However, there are different levels of protection, which all depends on the type of sealer you choose. Acrylics are decent low level protection with polyurethanes and/or epoxies giving excellent stain resistance.