I think it is a really cool piece of gear, and im very surprised that there are still so few reviews on it on YT. This gear allows me to drastically reduce my packsize, which is one of the things i like the most about it. I also love that it has the advantages of a bivy without the feeling of being confined in a small environment, and as the head is in the hood, i get plenty of fresh air, and dont need to worry about my breath creating issues with condensation. It is also pretty lightweight (mine is 500g, including stuffsack. The website states that it is a bit heavier) compared to a regular bivy + raingear, and still seems like it is pretty decent quality. It also has enough space that i can wear it over my 65L backpack (im not a big guy though). I am 170cm, and can fit my 30 liter backpack + shoes and jacket beneath my feet when i use it as a bivy, although this means that the bottom of the bivy will not turn with me as i roll over from one side to the other during the night, which is a bit annoying. Another downside of stuffing my gear in the bottom of the Bivanorak is that it means that i have to go out of the bivanorak if i need to pee in the middle of the night. Getting back in - and finding a comfortable position - can "wake up my braincells" enough that it can take some time to fall asleep again. I got it a couple of months ago, and since it is still pretty cold at nights here in Norway, i have only used it once so far, so maybe i just need to find the right technique.
I believe the Bivanorak would work much better with the "wearable sleeping bags" (or maybe just a thermal suit) than the regular sleeping bags. Then i could have my arms nice and tosty in the sleeves of the bivanorak, which would make sure the bivanorak moves with me when i roll around during the night, so i dont need to adjust the hood every time i move around. It could also save me the hassle of getting in and out of the bivy, if i wake up and have to pee in the middle of the night.
The biggest downside that i have noticed is that it doesnt work very well with sleeping pads inside it, and im not sure how inflateable pads handle being out in the rain..? Using a tarp and a groundsheet should work, but it would be cool if it worked without a tarp...