Yes, a 3D model is good to see the shape and geometry and may be used as a core to make a mold with...
3D printing is good for prototyping to test the fit for a design as you can print a part within a day depending on your 3D printer and it's capacity... The one at my first school took 24 hours to print the models...
After you 3d print it and make sure it will fit and work properly, then you can kick off making more durable tooling for the parts once you have verified the design is good...