http://www.outdoorresearch.com/site/advanced_bivy.html [nofollow]Excellent so it's turned up and looks good. The first observation was just how incredibly light it is. Where I've seen people complain about the weight of other bivis this one really does weigh next to nothing. I haven't weighed it yet but it's impressively light.
First impressions, it's fairly simple to get setup and fairly self explanatory. Getting it out of the stuff sack and consequently back into the stuff sack is very easy. It comes with 5 retaining rods which snap onto the body to put the hoops under tension. I'm debating whether to leave them snapped on or to take them off for fear of puncturing the material. It doesn't help that they're small and black which means losing them in the dark and any length of grass seems reasonably likely, presumably why they've given you a 5th spare. The reassuring label at the head end says "Leave unzipped at least six inches to avoid any possibility of suffocation despite being. The zips once you're inside are a little on the fiddly side and don't slide as nicely as they might. They're quite fine zips so I can see those getting jammed and caught in some of the material around them.
Getting in and out doesn't seem like too much of a drama and I like the low profile of the unit. I looked at the Terra Nova bivis and notice that they're alot higher inside, I don't get claustrophobic but I can see why others might find it so, enough for a lamp and a paperback though
You can also easily use the bivi without fitting the hoops so if you leave your sleeping bag inside the bivi if it all goes pete tong you can grab it out of your bag and dive into it.
I'll post a more full review once I'm back from Wales.