well, coming back to the subject at hand...
Nate I have a magnetic ballast driving my MH
, and there isn't any flicker after the bulb is started.
I'm using a mercury vapor retrofit bulb, so it has a special ignitor circuit that makes it flicker I believe.
Once it's buring, I notice no flicker at all.
I just wired a ballast similar to the one in that kit - so if you need help, just ask ... dunno if it includes instructions or not!
One thing 'against' magnetic is they are heavy - my ballast weights at least 10 lbs - I don't know of electronic are equally heavy, but they shouldn't be.
Finding something to mount that ballast in is a bit of a challenge as well ... since you want it somewhat protected from curious fingers or stray water.
All in all, building my own MH
turned out to be more trouble than it's worth, but it was still a fun project, and does a sweet job of lighting my tank.
175 watts for a 55 might be a bit of stretch, since the tank is 4 feet long correct? Maybe mounted in a 'tall' canopy it would work, or mounted above the tank and a spot light or something.