The general consensus is that the UCR is a little more finicky than a whoopie sling in having to do something to keep the tail taut. The degree to which that is an issue is, like most things in hammocking, entirely personal. What is objective is (1) the UCR is, for a long enough length, lighter than an WS make of the same cord, but (2) the truth is that the difference is quantitatively pretty small. If you're looking to be absolutely as light as possible then this is a way to shave some grams. If you're just looking to be lightweight then look elsewhere for larger weight reductions. For me the attraction is more a reduction in bulk. You might not much notice for Dynaglide, but I use 7/64" or even 1/8" Amsteel and I just like a slimmer package.
These days I'm inclined to eschew them both. Length of cord, lightweight ring somewhere on it as an anchor, around the marlin spike hitch and tie it off with a slippery buntline hitch. Minimized bulk.
except in cold weather when I can do the WS with mittens on!