The Clamp reflector only captures SOME light from the sides of the bulb but does not redirect any light fromt he tip. Spiral and Tube Type CFLS emit most of the light from the sides, not the tip or end.
There are reflectors that place the bulb sideways, instead of vertical, and they are more efficient, but not as portable and easy to move around as the Clamp Reflectors.
Lowering a CFL bulb down in betwen plants is ideal and a reflector would be almost useless then..