I'm sporting one too lawnboi, I have only spent a handful of nights in it but I like it. Simple, cheap,and light.i snapped and picked up an rei minimalist bivy this last week for the hell of it. Probably better options out there but it was a last minute buy. Its farily light for a completely waterproof bivy with a bug net, and was definetly cheaper than the big dogs. Should bring the temp down with my kifaru doobie to well below freezing. Being 100% waterproof it will also be nice to be able to roll my pad and bag right up in the thing instead of having to deal with stuff sacs.
I also agree with the what muleman wrote. I have a 4 season OR Alpine bivy and at first thought it sounded like a good choice for a lightweight all around shelter. It works and I'm ok on the claustrophobic feel but it is just not the most comfortable when getting in and out in a rainstorm, changing clothes or having access to your gear easy.While it sounds romantic to just have a 4 season bivy and nothing else. I find that I am much more comfortable and enjoy the experience more with SilNi over my head. When the skies open up and don't stop I just don't see how you can keep your bag and gear dry and change clothes etc... in a stand alone bivy. Not to mention cooking and eating.