"Of all your bivy's which one do you like the best? Do you use the Momentum one without a shelter? If so how does it compare to your Gore-Tex one?"
Hmmm. Hard to answer. First of all, the whole reason for my first sack (c. 1978) was the result of a traumatic experience on Mount Rainier with a totally saturated down sleeping bag. As they say, we learn best when we learn the hard way.
Goretex is a much heavier top fabric. As a result, I think I feel warmer inside those sacks. For a cool winter night, that works. I use these a lot for car camping when I am too lazy to put up a tent, but often I sleep on top of them rather than inside them. Back when I made these, there was no other game than Goretex. One is 1.5 and one is 2.0 pounds. By modern standards, those are a little heavy.
The newest one with Momentum is OK. I had designed it to be fairly light (I would have to double-check, but I think it is about 8 oz.). I had made it specifically to use in summer in Alaska, so I intended it more for light rain and humidity. I have no idea how it would be for heavy rain for a week. Also, it was done as a skill test. I bought my sewing machine only last December.
So, for a light and fast solo summer backpack trip in Yosemite, I would take the 8 oz. Momentum. For the same with one buddy, I would take only a shelter. For the same, except during rainy season, I would take the shelter plus Momentum.