Minimalist

This is about as basic as it gets. I bought this because of the price and my expectation for use on Summer climbs in the NW. It works just fine. A flap for the head aperture would be a great addition for foul weather. I use this with a BetaMid tarp, so that's not too much of an issue. As a stand-alone bivy I would prefer a little more protection from precipitation.

if you end up getting this bivy, you can't expect it to live up to sacks that are three times the price. but at the same time, i find it to be worth much more than the price i paid ($14 at the REI garage sale).

like the review above, it would be nice to have something to cover the face opening, but i've found my rain shell to work just fine. i've endured hard cascade rainstorms in this thing and not a drop got in. since the whole face area is open, i've never had a problem with condensation unless used in the winter with my rain shell sealing off any opening... and the condensation then was minimal. one night i didn't have my rain shell (it was a bad trip to forget it) to cover my face so i rolled onto my stomach to sleep, again, not a drop got in.

at 15 ounces it's not the lightest bivy but it's definitely not the heaviest.

i use it mostly as an emergency shelter during summer. if i think weather is going to come in i usually lug around my OR alpine bivy which is bombproof but heavy.

if you're on a budget and want to get something that will keep you dry enough, this is a great deal! or, if you tear up your gear quickly, this is cheap and sturdy!

I do not consider this a four season, although I have used it on snow, high altitude, and in winter. Sturdy material for being so thin and light- surprisingly so, as it has held up to a few nights on wet scree ledges/slopes where I was slipping and sliding with every turn. Never a hole, or a tear. It is noisy to sleep in. I've been outside a tent with friends and they complain I keep them up rolling over. In strong wind, you lose a lot of warmth around the face, and no protection against rain or snow, with frostbite possible around face in extreme conditions. Hard to sit up in it, and bugs can bite your face through the mesh unless you wear a cap with a bill to keep it off your nose and forehead.
All in all, great price, great value, durable, light, simple, and just don't plan on this for longer trips with iffy weather or the worst nights of the year. Adds 10 degrees of warmth to a sleeping bag only without wind. In wind, maybe adds 5 degrees warmth to the sleep comfort rating. "Convertable" bivy bags are a gimmick: the kind with mesh and storm shields will leak around the zipper for the shield, unless you are sitting up or hanging vertical.
For four season, or extreme conditions, I prefer the cheap army surplus woodland camo bivy bags. Heavy, and no mesh, but you will be dry and can leave it out all day even in a rain or snow.