hortilux is a generic term for a "plant bulb" there are probably 20 hortilux 400w M59 bulbs...
My personal reccomendation would be the EYE lighting bulb, namely Iwasaki...
EYE Hortilux Metal Halide
EYE Hortilux Ultra Ace
EYE Hortilux BLUE
Hortilux is a sales pitch, not necessarily a determination of the value of the bulb. Especially when viewing plants is concerned, I reccomend a bulb you can live with looking at the plants. This means a bulb with a relatively "cool" temperature in the 4000-6500k range. Also the Photosynthetic Active Radiation is different for various bulbs. The more green, the less useable light the plant has.
My personal favorite in a M59 quartz bulb is the Iwasaki "clean arc" 6500k bulb, it has a CRI of 90, meaning near perfect color rendering which is important for actually seeing the plants accurately. Also has the one of the highest PAR rating of any bulb.
EYE CLEAN ARC - HIGH COLOR RENDERING (DAYLIGHT)
There is a lot of glimmer and glammer in bulbs, lots of hoopla and false information. A decent bulb will grow just about as good as any other, and there' no reason IMO to spend the extra money on a "hortilux bulb" because they're not necessarily any better.
Here is a good article, you can see some of the "hortilux plant bulbs" indeed are worse that a good Everyday use Metal Halide bulb! There are so many other factors which will decide the health of the plant than color specturm, people make a lot over nothing. Priority wise, the Amount of light is first (i.e. wattage and lumens), second the reflector, third the distance and temp, and only after all those factors are optimized would I even bother with spectrum. Just because it's easy to buy and plug in, means you're probably not going to get a huge boost from changing one bulb for another "hortilux". A new bulb is good, but from one to another decent bulb isn't going to make a huge difference in my experience. It would be impossibly to quantify anyways.
Aqua Botanic-light bulb comparison