MH has been good for my seedlings so long as I maintained good spacing. A 250W MH is not a bad choice for seedlings and early veg imo. That's what I had ... the only issue is wastefulness until your canopy gets larger. cn
50% is plenty till you get more leaves - get it as close as you can ,use the top of your hand as a guide when it gets uncomforable then your too close
what are you growing?
imo its a waste of energy and useful bulb hours. your seedlings arent going to absorb even half that even with it dimmed.. but I mean if you have it and dont have a flouro laying around then use it but like moon said at an appropriate height.
sensibility with distance and knowing that these little guys are just babys! fluro's are usually the safest bet for those little guys, then moving them to an MH after they have gotten a little stronger.