My friends and I love to go adventure swimming, fully clothed of course because we're tough. We each wear a small backpack with drain holes and a waterproof pouch for a change of clothes, food, and of course a Bivanorak.
When we swim along the shore of Lake Zurich, we stop for a break when we come across a nice beach. There we put on the Bivanorak over our wet clothes to keep the warmth in and the wind out. It is really snug and warm.
After the break we shake the water that dripped from our wet clothes out of the Bivanorak, roll it up into the backpack, and jump back into the lake.
At the end of our swim, we use the Bivanorak as a portable changing room to get into our dry clothes. Then we're ready to head back home, feeling great.
I've have used a bivanorak for years. It's great value for money considering what it is and what I can do with it. A poncho is great but the bivanorak gets rid of the things that one does not like about the poncho.
The one feature that is better than a poncho is that you can wear your backpack on the outside as well (if it too has a rain cover or is waterproof) and it's not uncomfortable.
It will also compress to almost a third of the size of the stuff bag in comes in. I have a really small compression bag that will fit it, and it's not much bigger than a soft-ball.
Downsides include no tarp options like a poncho, and doesn't vent well. It is best for the three colder seasons, with a poncho the better hot weather solution.
They are great kit. Expensive, yes. Need a TALL size, yes. But it is what you would get if you take a Cagoule to the extreme. Since it's made by Hilleberg it's tough as nails and top end quality. Made in Sweden, but you end up paying for it.
I've owned a lot of camping gear over the years. The Hilleberg gear is so far out of the league of what you typically find that it's a great value.