While they may look the same notice how much more grease the Lemforder has.

Also notice the clamp there is on the moog above, and the clamp that came with this Mercedes upper ball joint kit, tie rod boot kit, and lemforder lower ball joint. While the picture doesn't show it very well, the above items use a piece of flat spring steel to use as a clamp. The moog uses some round POS that let my boot come off before the spindle was even on the car! The MB clamp takes 5X the effort to put on, therefore it takes that much more to come off. :)

The deciding factor for me (before I knew about the spring and grease) was when searching the same question I found that omegabenz had a problem with his moog balljoint/s after 10k miles, since he has switched to lemforder and had no problems.