Design patents protect a product's look, not its structure or function. (A utility patent does that.) Design patents are perfect for one-shot, short-term products, since they're simple and inexpensive to file ($155 vs. $380 for a utility patent). The issue fee (the fee you pay when your patent is awarded) is $215, compared to $605 for a utility patent. More important, the design patent application is simple, and usually no attorney is needed.
Since design patents protect only the appearance of a product, they won't stop a competitor from copying your product's mechanical features in a different design. However, a design patent does allow you to put "patent pending" on your product. When competitors see those words, they won't know what type of patent you've applied for and will typically delay introducing competitive products. For a short-term opportunity, this delay is all you need to gain a competitive edge.