I love mine. Here's what I know:
I have the Anorak version, not the hooded version. I use it to bike and run, and I will use it to backpack. It makes a good spray jacket, like if it's drizzling on a bike ride or if there's a lot of snow kicking around. I have taken it out in drizzles, and it hasn't wet through, but if I take it out of the washing machine, it's holding water. It air-dries in about 20 minutes.
It's very comfortable, but I got the large and the sleeves can ride up a little bit. I actually prefer this, because I don't have a good chance of tearing them on anything.
My L weighed in at 2.3oz on another site. I have no scale.
Packed size is about 1.5in x 3in cylinder. Like one of those mini V-8 cans, maybe a bit narrower.
The seams are not taped. I bet you could seam-seal it. The zippers are not waterproof. I have used it in the rain, but if it was more than a drizzle or if I had to stand in it for longer than 20 minutes, I'd get my raincoat. This is not a raincoat.
The windproofness is top-notch. It's an extremely tight weave. I can't compare it, though, because it's my first windshirt.
All in all, I give it 9.5/10, it's one of my favorite items, but YMMV