I would gave bought a Grainger for my HB JB build, but the string spacing was wrong for me. But I did get my Hipshot bridge from BTN. A lot of my Hipshot kit has come from them. Always had good service and when I got a duff tuner with a very stiff section, they immediately just sent me a replacement without having to send the original back, which arrived the next day.
I must say that the Grainger certainly looks machined whilst the Sung Il looks cast. One may have certainly inspired the other.
I can attest that the Sung Il is cast. The Grainger website says it's milled on a CNC machine. It looks like about as good an option as I have seen in an alu locking bridge, and certainly competitively priced with the Hipshot...which is the only other alu locking bridge I can think of. Of course, I haven't seen one for sale by a US seller, which undercuts price-competitiveness for me at least....