Just for the record, I have no connection with Icecap, which in any case makes some of those cooler electronic MH ballasts you mentioned. My comments were based entirely on my experience with my own aquaria, and observation/discussion with other aquarists. I admit my experience with MH is limited, and over a decade old. Perhaps great strides have been made since I used MH. Certainly, better MH color temps have been developed, particularly by the Germans and their imitators. Nevertheless, I notice that most MH applications seem to position the bulb rather far from the tank's surface, and MH users I know tell me they have higher evaporation rates with MH. Naturally, a covered aquarium will evaporate less water. In my limited experience, an uncovered MH tank evaporates more water than an uncovered VHO tank, and a covered MH setup will get hotter than a covered VHO, unless the MH is suspended well above the tank, an arrangement presenting it's own set of problems.
Most of the MH fires I've heard about were connected with ganja growers. I do think the high voltages and super hot temps of MH require more care to see that they are, as you say "properly set up". Maybe I'm too conservative, but I would feel worried about leaving MH unattended for a couple of weeks, just like protein skimmers, which I shut down if I'm going away for any length of time. My VHOs, which sit almost directly atop the cover glass, seem to need almost no attention, other than cleaning the bulbs and cover glass periodically. I'm not sure about wasted spectra when comparing one type of bulb to another. I do not pretend to be a lighting engineer, but neither am I totally uninformed. There are many kinds of flourescents, and a variety of MH bulbs as well. I am also not confident that we absolutely know, in terms of the needs of reef animals, what is "wasted" and what is not.
I am not really attacking metal halide lighting. I think nothing looks quite as spectacular over a reef tank, or is as effective in deeper applications. I do think they require considerably more attention, and have a few safety drawbacks, particularly around pets, small kids, etc. I was responding, in this string, to someone who had already ordered (it seems) a VHO system that is quite powerful, and, I think, more than adequate for the application described.
I've kept reef animals for several decades, and have my own opinions about the art and science involved. It's mostly art. The simpler the better is what I have come to believe, and most of the cranked up "high tech" devices marketed for reef tanks can be safely removed and tossed in the trash. Most are anodynes sold to people who are having problems because they have not developed the skills and the art of aquarium keeping. They run into problems, and are convinced that some gadget is all they need to set things right. An aquarium well stocked with healthy live rock will stabilize its own dynamic balances if the aquarist does not over meddle, and has developed a good skill level. But that is another topic.