I've only used the tube version, as a rear tyre (1.9) for trail riding.
The first one was a kevlar beaded one and it was surprisingly grippy where I ride (loose over hardpack, gravelly and rocky singletrack) I had a few flats at one stage and blamed the tyre (they are very light) but after that no more, so I must have just had a band run. The tyre rolls well and the light weight can be felt. It wore very fast, I only got a couple of months out of it riding XC.
I got a wire beaded replacement which, while still labelled a 1.9 was slightly thinner. All else was the same - including the rapid wear. No more flats with this than any other tyre.
I believe the tubeless ones are 2.0 and have a slightly different tread pattern to the non UST.