I'm guessing the SM4 is, as the name indicates, is an actual array of four LEDs in surface mount configuration. Either all four in series or 2x2 for the 6 volt version. I have a pile of the older 360 series that are similiar. Fantastic color at 3000k, but horrendously inefficient compared to today's emitters. These newer SM4's are better, but still lag the premium competition in terms of efficacy.
Then again Bridgelux is competiting with other Asian firms in the fixed lighting market only, and like everything else in the Bridgelux universe the SM4 is likely cheaper per lumen than the competition. The higher voltages are common sense. Their bigger arrays come in nothing less than 20volts, which is a bear to drive with batteries unless you're a boost freak, but very convenient to drive from 120volt mains.