So if Halides only grow algae they can't grow plants then because plants are not alage. This is horrible advice, plants grow like mad under metal halide and it's one of the most efficient light sources you can find. If you strike the right balance guess what, no algae. Granted, these halides are very bright, and in the wrong hands you could easily get way too much light, and burn the leaves right off your plants, or have heat issues because all that wattage will get pretty hot, or become the greatest home algae farmer in your neighborhood.
The individual reflector t5 light will probably be as bright as a metal halide, but when it comes time to replace bulbs, you will pay far more on all those t5 ho bulbs. Finally LED's, good ones, are just as efficient, but far more expensive for an equivalent amount of light output.