Dual Spectrum rocks! Ever since changing a few years ago, I would not even consider going back, the plants love both lights/spectrums together. I have recently started to veg under CFL and tubes, seems to be working ok, albiet slow. I would like to up the size to a 600HPS for more penetration eventually, but my dual 400/400 bloomroom works great for now. Remote out the ballasts to cut down on heat. Cooltube and a good fan is a must though in my small space. Putting my hand underneath them, it feels like the HPS is hotter - but its also a larger diameter and closer to the glass then the MH. By rule of thumb, MH should be hotter at = wattage