digital ballist for MH and HPS

Does a digital basllist work for MH and HPS?

Nearly all are interchangeable. So, yes.
Usually a digital ballast will power a MH and/or a HPS equally well.
They also power Mercury Vapour (obsolete now) and Duel Spectrum (very popular).

Yes , They work for both. Easy on the electric bill too. My electric bill this month was $111.00 . That's for a three bedroom house with two kids leaving the lights on all the time and TV's in every room. My 600w ballast and fans running 24/7 cost maybe $20 a month.

Yes, but they recommend a bulb designed for a digital ballast. They cost maybe $10 more then a regular bulb. I recommend the Genesis. It's dope. You can sync up to 6 of them on the same remote, they have sunrise function, and they will alert you by alarm if there is a problem in your system (though that has never happened to me )