I don't have the U, but the V is underwhelming. I bought it as an upgrade to my 952V, and both are lacking. In fact, I don't know Surefire makes any decently outputting V version.
I need the infra anyway so kept it, but the U I'd suspect is much better as a white light.
I also have a 300V which is worse output than the 600V in both white and infra, fwiw.