I have the M series. I haven't had a problem with it. Although Ultraflix is not in the preferred apps when you press the V button, it is the very first app that appears when you go to the Yahoo App Store. It has a banner that says "All 4 K Content". It streams fine, but sometimes I have to go to UF settings and change my download speed so that it doesn't stutter. Once I change it, it works fine.