Ballast choice for Ushio 400w

[Aquattro]

I'm aware of the problem with them blowing up, but I read on RC somewhere that it was restricted to certain batch numbers. I had one blow similar to Marc's, but it was almost a year old when it blew.
According to Paul from ahclighting.com, the HPS ballasts were better, light wise, than the M135. The M135 just helps the bulb start, but does nothing for the quality of light.
Switching to Iwasakis isn't an option; I tried one on my tank and was really unimpressed with the color. I don't have enough room to add sufficient actinics to compensate! :P
I can get the Son Agros for $86, so I might try those, unless someone suggests a reason why the S51 is better.
I did notice the ballast to lamp distance is only 2 ft. with the S51, so that might disqualify it right away!