the 6 hours of light lets the plant actually grow properly. Plants need rest to, and when they wake up from rest to do their work, they do it beter.
If you decide to purchase a HPS bulb, you will need a ballast. They should be bought together from the same supplier. They have to be able to work with each other.
You dont need a MH for veg and HPS for flowering, it would be nice to. It is not a must.
If you get the 430watt son agro, It has the added blue spectrum(for vegging). I did my plant with that one light and nothing else. I cant complain, noone else will either. The bud is DANK and I got LOTS. Well worth the investment. I got all my money back(from lights , nnutes, equip) and 2 ounces to smoke.
Im glad to help.
I think i paid 245$ canadian for my ballast , bulb and reflector. I dont know how much that is american, probably around 3something?