Most porch planters are bought in pairs and placed either side of a door, and the mistake people make is buying to the width of the step rather than to the height of the door. A planter that looks generous on the ground disappears against eight feet of doorway. As a rule the planted height, pot plus plant, wants to reach somewhere between a third and a half of the door height, which usually means the planter itself is at least two feet tall before anything goes in it.
A porch also asks two things of the material that a garden bed does not. It is often exposed, so the planter takes wind, sun and freezing weather with no shelter, and the fiberglass here is non-porous, which means it does not take up the water that expands on freezing. And it usually sits on a finished surface. That matters for drainage: a drilled planter will drain onto whatever is underneath it, so on a painted or timber porch either leave it undrilled and water carefully, or plant into a nursery pot inside it and lift the pot out to water.
Weight is the other porch-specific point, and it works in your favor twice. These are light enough that one or two people can carry them up steps and position them before planting, and heavy enough once filled that they stay where they are put. Concrete or stone at the same size is a different proposition on a set of front steps.
