Sierra is a coolant/antifreeze. I think Amsoil's coolant/antifreeze is the same kind of low tox antifreeze. But the bulk of what is in West Marine is an antifreeze only for winterization. Not for using in the engine when the engine is running for the summer. Typically the pink RV stuff is used for the fresh water systems in a boat and the more expensive stuff with better corrosion properties is used in the engine. But many use the pink stuff for everything.
While manifolds, risers and engines fail from corrosion, I would bet the amount of corrosion that happens over the winter is tiny. Corrosion is chemical and less happens during cold temperatures like the winter. Salt water is what causes most corrosion.