It's quite useful because you have a range of densities to choose from in one filter. But I hope you know about the cross patterns when turning to higher densities. Correct me if I'm wrong, but I think all Variable ND filters have this problem, no matter what price range it is. It's gets even...
Far Horizons
Shot with Haida 10 stop ND, 30s
Bridge over Humbled Waters
Shot with Haida 10 stop ND, 30s
Come Fly with Me
Shot with Haida 10 stop ND and cheapo Tianya 4 stop ND, 5 mins