The Markforged continuous fiber prints are very strong so can be used structurally.

As for confidentiality an NDA will cover you.

In case you want to go the expensive route and use online services like Shapeways, they also guarantee confidentiality:

You, as a designer, retain all your intellectual property rights in your 3D design, including without limitation any and derivative works like 3D renders. Except for the rights and licenses specified below, Shapeways shall not use, modify or display your 3D design or derivatives thereof