The bulb is superior to almost any other your going to find and is so because it not only contains the red spectrum used for flowering but a ample supply of violet blue and green for max vegetative growth during flowering which results in more buds. It is expensive but if your going for the best this is pretty much it.
i however use a cheaper alternative that ive been quite happy with, its a HPS bulb with built in 30% blue spectrum its much cheaper and ive gotten some really amazing results with it and so has my friend. heres a link for you