One of these mounted on each foot with a radio controlled trigger (we could call the trigger a mouse), would be sufficient to jump the lander off the comet and let it relocate. After all on comets it's location, location, location.
I think your example confuses weight and mass. The initial speed imparted to a craft by the suggested mousetrap mechanisms depends on the mass of the craft, in this case ~100kg. The height attained due to this speed is then independent of the mass. As Galileo noted, any given mass may be considered as two smaller masses conjoined, and hence the motion of objects in a gravitational field must be independent of mass ( in so many words ! )