Hydro-Shield, Does it Make Sense?

Hydro-Shield is a skeg-mounted hydrofoil that fits on most outboard and inboard/outboard (stern drive) motors, protects your boat’s propeller from underwater impacts, improves your boat’s performance, and shields marine mammals from injury.

Guaranteed improvement in overall performance and handling

I would think the top speed would go down? But they are saying the cruise speed is improved.

Hydrodynamic drag.
More surface in the water, just like the wings on top of the props.

I read all of the reviews. Unless they are writing their own, the thing seems to work.

I'm just trying to figure out the hydrodynamics as to why it would?