By "performance" they mean thrust, as opposed to ISP, as suggested in the comments. There are far more mass-efficient engines than theirs that are already in use eg: ion thrusters.
Their VR900 engine has 900lbf thrust900 lbf thrust. Compare this with 99lbf for Chandrayaan 1, 110lbf for Clementine, and 0.015lbf for SMART-1.:
- 99 lbf for Chandrayaan 1
- 110 lbf for Clementine
- 0.015 lbf for SMART-1
Their "competitors" are pretty much everyone else who launches a probe: Chandrayaan 1 made 5 passes of the Earth over 13 days to enter a trajectory that reached the moon, Clementine took 3 weeks and 2 passes to get to the moon, and SMART-1 spiraled out over 13 months.