Hello Peter,
thanks for sharing this very interesting post on the Double Hourglass Antenna and the design considerations behind it. The progression from the double-quad to the SHA and finally the DHA was particularly insightful.
I have built the antenna meanwhile and was able to get it on the air last weekend. The design is straightforward to reproduce, thanks to your excellent groundwork, and it works well in portable use.
I made a couple of small adjustments to suit my setup: the mast mounting solution differs from the one shown, as I designed and 3D-printed a version specifically for my 6 m squid pole. Also, I had to make the wire elements about 2 cm longer, since I used standard 2.5 mm² speaker wire from a local hardware store.
The field test was done during the DARC VHF contest last weekend, where the DHA showed a solid performance. I brought a 6-element yagi for comparison which was mounted on a second pole, about 4 metres above ground. In other words, both antennas were approximately at the same height.
Most of the time, I used the DHA as the main antenna without even turning it. I tried to work what I could hear and only when signals were marginal, I switched to the yagi. In many cases the yagi produced stronger signals if aimed carefully at the other station. This was to be expected.
But interestingly, all QSOs with Italian stations were made using the DHA, which consistently produced stronger signals in this direction. Possibly knife-edge diffraction along the alpine path plays a role here…
Conclusion: The DHA is easy to carry and set up in the field. It’s a nice compact option for those looking for a bit more gain on 2 metres without adding too much complexity to their setup. Its wide horizontal beamwidth reduces the need to turn the antenna largely.
Building the DHA and discussing the details was lots of fun. Thanks again for bringing up this idea!
Last but not least, I would like to thank you for the first S2S and DHA-2-DHA QSO yesterday across 270 km 
73, Roman