I started to look at other options and quickly narrowed it down to two alternatives: The Tarptent Double Rainbow and the Six Moon Designs Lunar Duo. The nature of these tents also quickly made me dismiss the option of a tarp and a separate bug netting, which I've always found cumbersome and not really as light as one would believe. Since then a number of other ultralight designs have emerged, but these were the main alternatives back then. The Lunar Duo is slightly bigger and in some ways nicer, but it needs either walking poles or two extra poles to be erected, which I don't have with the mountain bike. Additionally, some reports indicated that the Double Rainbow could take fairly hard winds, which the Lunar Duo with its larger wind surface would have problems with.
The choice was made and I ordered a Tarptent Double Rainbow directly from the manufacturer in the US. It was not seam sealed from the factory, so I seam sealed it according to some instructions found on the web, after which I erected it on my back yard for a rainy night to test it. Two spots in the seams still leaked, so I applied some more seam sealer. It has been kept the water out since then. After seam sealing the weight was 1150 g.
The first test in the middle of August showed it to be exactly what I had wanted. A beautiful evening and night, with lots of bugs and no rain. A bug shelter with good views was all that was needed.
The tent can also be pitched in a slightly more open configuration, for the occasions when it rains but you still want to keep it airy. I haven't used this feature much, though.
There is also a separate liner for the tent, which makes it pretty much a double wall tent. I also bought that one, but in practice it doesn't work well for me, since it steals too much space from the otherwise sufficient head room. I've also used the tent a few times during the winter in really cold temperatures, but there are certainly better tents for that purpose.
Perhaps the most interesting question with an ultralight tent like this is how well it copes with wind. Do you dare take it to the mountains? I've used it in winds with gusts probably a bit over 20 m/s, but I've been reluctant to erect it in the most exposed places. I think it is pretty clear that the best tents can take more wind, but I also think that lots of people take tents into the mountains that can take a lot less than this one. One aspect some people might not like is that it is more drafty than completely enclosed tents. You can reduce the drafts by pitching the wind side as low as possibly, but it is still more airy than e.g. a Hilleberg tunnel tent.
Any drawbacks? I've been really satisfied with the tent and have a hard time coming up with any real drawbacks. It is not freestanding, a feature which have become more important to me now that I do more kayaking, but the only improvement that would really matter to me would be a completely detachable inner tent. A detachable inner tent would make it possible to keep the inner tent fairly dry over many days of raining.
To sum it up: I do like the Tarptent Double Rainbow a lot. It has been what I hoped and expected it to be. Would I buy it again? Quite possibly, but I would also take a look at the other options currently on the market first. The Hilleberg Niak 1.5 does for instance also look quite interesting, and there are certainly other options as well.