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Very true! If you are flying in a fairly "clean" signal area, it will increase signal strength, help block signals outside of your antenna's "view" and can give you quite an extended range. Not everyone flies in "clean" signal areas though.
They will ALWAYS improve transmission, but that doesn't mean that they will necessarily still be able to "punch" through extremely heavy band traffic, and doesn't do anything to make the drones signal directional either. Have to receive as well as transmit.
If it works for you.. that's great! You're not alone. But for many, they won't. And they aren't wrong either.
Fly on!