I have only tried using the DD as a bivi once to try it out in my back garden.
As I did not want to risk damageing the bottom ( my back garden is grass but I would not call it a lawn ), I put a CCF mat on the ground first and then had the DD on top of that . I used hiking poles pegged out to set up a ridge line and then hung the hammock using the supplied elastic cord. This had to be quite tight. The ends of the hammock where also lifted with the normal black tree huggers onto the hiking poles.
I then put my self inflating mattruss between the double bottom.
With a second set of poles set just a bit higher I then rigged up the tarp to cover the lot.
This setup "cost" me a self inflating mattrus and a set of walking poles over what I would use for a normal "tree" based hammock.
I then slept inside the silk liner and had my sleeping bag as a quilt ( as I do in my hammock as normal.
I did not sleep as well as I do in the hammock as normal. A few times I had to adjust the sleeping bag quilt but soon dropped of. That being said I also sleep much better in a hammock than I used in a tent.
The result was I did sleep and keep dry. The hiking pole ( a £6 3 piece no name) at the head end did slip down a bit. Was this due to the weight, me turning or just not been locked tight enough, I dont know. The sides of the hammock would have stopped ground water coming in but as it did not rain and I was also covered by a tarp, I am not sure it was a real test. As the photos were also rubbish I did not publish the test.
The result is the DD does work as a bivi but a bivi is not for me.
A pair of fibre glass tent poles might be a better idea as supports than 3 piece hiking poles. The pair did work ok for the tarp ridge line mind.
If I was to sleep in a tent these days, I do think I would use both the CCF mat and a self inflater in any case. This could also be because I already own both?
The last Hike I did was from YHA to B&B and back. I would have to think long and hard about using a bivi, DD or other, as a matter of choice. There is a camp site nearby which does not have trees or poles in the main area so I could and have considered using the DD and tarp as a bivi tent but only in the spring/summer. Not your wild camp at all I know.
In short it did work and its a free feature on what I think is a great hammock. There is no way I would buy a bivi but the DD can be used a stopgap if you wish.