I used my WBRR with spindrift at the Frozen Butt Hang up here in MN. I used 2 UQs (0* Incubator and a 30* home made UQ) I also supplemented with a very light windshield sun blocker that I worked in-between the layers.
I had 2 TQs covering me (0f Burrow and a 40f Thermarest Ventra)
The first night hit a low of -9f. I zipped the spindrift up completely and the next morning I noticed a lot of frost inside. I sorta kicked myself for not leaving a breathing hole to prevent all the frost.
The second night (17f) I left a large breathing hole and had almost no frost build up. I got a bit warm and jettisoned the 2nd TQ.
The third night was cold (-15f) and lots of wind. I figured that it was probably worth the risk to zip it up completely and hope my frost bib would do it's job. I woke up to a huge amount of frost inside, again. By the time I got myself organized and out of the hammock, everything was covered by the frost.
I am sorta realizing that I need to leave a fair portion of the door unzipped in the deep winter, but I can't wait to use it in the spring and fall.
I really like the ability of the Spindrift to cut the wind. It makes for a peaceful sleeping environment and it keeps it dark so I can sleep later