Great price on GoreTex. I'd want to know what the bottom was made of, too. (Probably coated nylon, but it never hurts to ask.)
In that same price range, if I were looking for a bivy, I'd also consider the REI Minimalist. It's about a pound lighter, full side zip, and has a mesh panel over the head and neck area. However, it's a proprietary W/B fabric (Elements?), and there's no W/B cover over that mesh opening. So, it's designed for use with a tarp, not out in the open on its own. However, a good product at a good price - before lightweight tents (like the MSR Hubba line, Big Agnes offerings, and TarpTents) came along, I used a Minimalist a lot with a tarp. Now, I'd never even think about using one.
You made an excellent choice with the Moment, given what other folks are saying and the general reputation of TarpTent products.
Oh, but my TiGoat Ptarmigan is only 7 oz. and $110 with netting. Besides, you have a Moment, why do you need a bivy? I'll tell you what, I'll swap you my bivy for your Moment. Save me the trouble of selling my Lunar Solo.
They can be had on ebay, brand new, for about $64.00 shipped. Just search "MSS bivy". Just ordered one because I want a very roomy, bomber bivy that I can throw directly on the ground. GTX is not the most breathable material and I expect to wake up with condensation. But I plan to use it mainly for simple one night trips.
From what I can gather, the military has switched to a new digital camo pattern and the old woodland camo sacks are flooding the surplus market.
_________________________ If you only travel on sunny days you will never reach your destination.*
* May not apply at certain latitudes in Canada and elsewhere.