The rod-like shape means that porridge can be stirred without congealing and forming lumps, unlike a spoon that would have a dragging effect during stirring, and the low surface area reduces the chances of porridge sticking to the instrument.
Spurtles are made from wood, including beech, cherry wood, and maple. They come in a range of sizes. Traditional spurtles have stylized thistles at the top, while modern ones often have a smooth taper.
The custom is that a spurtle should be used to stir in a clockwise direction with the right hand. Counterclockwise, or with left hand congers up the devil.
My spurtles are finished with a food-safe durable wax/oil.