Yes i've used it but you don't use Ultraviolet to stream or watch any content downloaded onto your computer or device, you are directed to Flixster where you can stream any movies in your collection which seems counter intuitive tbh.
I've tried streaming the only movie in my collection which is Sherlock Holmes 2 and it was quick to buffer and start but the picture quality was not good atall but then that's the case with most streaming services i have tried but when compared to the version i have downloaded onto my computer and iPod touch it's shocking.
The downloaded version is the best way to watch any Ultaviolet digital copies but i'm still not happy that you can't use iTunes as all my movies via this one and The Inbetweeners movie are on iTunes and the ease of use and picture quality is superior to Flixster/Ultraviolet.
The feature to change your copies to play from Ultraviolet is yet to go live so i can't compare the two, the box on the ultraviolet site that enables you to do this when you are signed in just says "Available Dec 20" which is a way off yet.
Hope that helps.