If the ballast has the part label on it, it's pretty easy to tell whether it's HQI or not. The dual 250W HQI part number is AQ2-250HQI-120 (or something similar). The M58 ballast is AQ2-250MH-120. If the part label is missing the only way I know of to check is pull the heat shield and check the parts inside. If that's an HQI ballast it's a smoking deal at $100. With sockets and lamps it's steal a great deal as a starter setup for $100.
In my opinion, PFO made the best metal halide ballasts ever. I tried like crazy to find one of the 250W HQI when I upgraded but couldn't so I ended up getting a Sunlight Supply Blue Wave 7. My understanding is that when PFO got pushed out the folks went to Sunlight Supply. Someone can correct me on that if I'm wrong. Anyway, PFO gear is bulletproof and so far my Sunlight Supply stuff has been as well.
Mike