I used to take Dark frames all the time with the Orion SSAG, but in some areas, it just could not detect a star, or if you COULD see one, half the time it was not bright enough and lose it with seeing fluctuations. I have yet to NOT find a guide star with the Lodestar
With the Orion, I had to REALLY change a LOT of PHD settings to get it to reliably guide. Aggressiveness, pulse duration, hysteresis etc etc.