| It isn't really an issue of efficiency, but of the distribution of light produced by the different shapes. Parabolic reflectors produce, at best, a completely focused beam of light the same width as the reflector. The reflector you show is of course not deep enough to focus all the light but it will produce an intense central zone of light and then a spread outside that depending on how far away it is mounted. Conic reflectors produce a more even spread of light across the whole illuminated area, and this will vary with the distance from the reflector to the plants. Because the sides do not curve down around the bulb they generally need to be wider than a parabolic reflector. Interesting that both reflectors are painted white on the inside. Not sure what the white coating is but generally it is hard to improve on aluminium and hard to imagine a white coating which won't fade mounted so close to a metal halide. Perhaps they have used some form of powder coating to avoid specular reflection, not really sure what's going on there. The other point to make is that this form of reflector is usually designed for vertical mounted bulbs which are not so common these days. I didn't see anything in the blurb, make sure your bulb will be suitable. | 
