I use ULS almost exclusively when using clear glass. I only use UL when I am using 0.030" clear...in other words, when I am using a kid bow. When I use black glass, I use ULZ...even when using the thin 0.030."
I believe the difference in 0.040" UL and the 0.043" ULS is minimal in weight. In 0.050" UL vs 0.050" ULS the weight difference of the scrim is practically non-existence. It takes a square yard of UL and ULS to measure a very very small difference in weight. The amount in a 1/2" wide limb tip (the part that moves the most on a longbow) is so minimal I feel the scrim adds durability and stability.
That said, there is nothing wrong with the UL glass. I just think ULS does everything just as well as the UL but it adds some additional benefits in stability and strength beyond my personal abilities of measure. My reason for preferring the ULS and the ULZ is largely based upon testing results done by Gordan glass. Their test data is on their website.