There are more durable and more comfortable rain wear, but none as light. The O2 jacket with hood weighs only 6 oz (175 g)! Pants are about the same. Its featherweight can slip in anywhere without notice. This makes it perfect for backpacking or bicycling where ounces and bulk count. Rather than using the usual Goretex-like breathable fabrics this uses a 3M Microporous Film fabric which is thinner, lighter and cheaper. The fabric does not feel plasticy, like most lightweight ponchos; instead it feels almost like a soft paper towel. It is perfectly waterproof, even in severe downpours (I even tested it in the shower once; my clothes dry underneath). And fairly breathable. I will wear it as a windbreaker on hikes even in sunny weather, and not sweat.
The garment is minimal and packs small; simple zipper, no pockets (on the basic model). Being so lightweight it is not as robust as more expensive gear — but perfectly adequate for unexpected rains. If you plan to wear it over heavy outer wear, order a size larger.