Let the design and engineering of your product to be made by the same professional studio and avoid bad surprises! In fact, think about the case in which you decide to entrust the engineering of your product to more than a studio or a professional: this creates a continuous and unproductive information rebound between designers and engineers.
When one realizes printable 3D objects with injection plastic, a good engineering considers the exit print drafts, the gauges, etc. A good design is made by a good product realization.