How to protect the design of our products

In the U.S., a design patent only protects aesthetic or ornamental features and cannot be indirectly used to protect the functionality of a particular design (that is generally what a utility patent covers). Trade dress protection, available under the Lanham Act 15 U.S.C. 1125, can protect the shape of a product or its packaging. Whether either design patent and/or trade dress protection is appropriate (or available) would require evaluating your proposed design against the backdrop of prior art and product/packaging designs currently being used as source identifiers.

You are correct, you can obtain protection for your drone design via a "shape" trademark or a design registration/patent. Speaking from an Australian perspective (which would also generally apply to most jurisdictions), it is much easier securing protection for your drone design via a design registration/patent compared to a shape trademark. The tests that need to be satisfied in order for a shape trademark to be granted for your drone design is more stringent than for a design registration/patent. However, one advantage of obtaining a trademark registration over a design registration/patent is that trademark protection may continue indefinitely (subject to certain conditions) whereas a design registration/patent has a fixed term, for example, a maximum of 15 years in the US and a maximum of 10 years in Australia.