Product Design and Development vendors help to augment your current skills or to fill a gap of a missing skill during product development and manufacturing. The companies can be involved in any step or the entire process depending on their capabilities and your needs. Mechanical Design and Industrial Design vendors can help with the design and look of the product. The design firms maybe involved from the very beginning at the prototyping stage or be engaged later in the process to help polish up the final design.
Some firms have expertise in a specific area instead of a service. They may be able to help with the entire design, look and manufacturing process of electrical systems or medical devices. Others will only specialize in helping develop the manufacturing process. Reviews for all the different types of Product Design and Development vendors can be found on VendOp.