The electronic ballast are more efficient and supposedly will fire any bulb(mogul or HQI). They supposedly run cooler, however, I have never ran one, but I do know that my Hamilton ballast gets pretty hot. Not hot enough to start a fire, but I wouldnt hold my had on it too long, and when I open the door to my stand, its probably 100+ in there just air temp.
BTW, I dont think(i could be wrong) Hellolights M58/57 ballasts are boxed either, so you would have to get a box for them and wire them up, since you just get the raw components. If you have the money, I would go electronic. You can get a 250W Icecap for like 125 and the hellolights/ARO ballast for 139, unless it goes on sale.
50gal cube in the works.
2x250w Coralvue eballast and reeflux bulbs for sale.