The problem is anything that works uses L-rods also known as body response devices. It takes years to really learn how to use the rods. Almost nobody learns. If the antenna pivots/moves it will be very difficult to learn. The frequency generators work if you can learn how to use the rods.
I'm working on the Contraption which uses the frequency generator principles but does not use L-rods. You aim the receiver and it beeps when pointed at the selected target. It's not perfect. Some day I hope to find someone interested in it that can finance some design changes, build some inventory, and some advertising so it can take the market by storm.
https://www.youtube.com/watch?v=O0FIE0mGg7k