I bought one of those for my first grow. It's expensive to use, but since I have it installed in my current room I still use it. They are used for the seedling and vegetative growth stages of your plant. They can also be used for flowering. Mercury Bapor lights have been almost replaced by Metal Halide lights. You can get up to 8,000 lumens from one bulb.

I'd start looking toward CFL bulbs for the vegatiative stage as they cost a fraction to run compared to one MV bulb. Then you'll need better light to get good buds in the flowering stage. I went the HPS route.

Have fun!