Will Flash Activated Slave work?

Okay. I'm currently doing portraits with a Nikon SB-600, a shoot-through umbrella, and a Nikon SU-800. I want to get some monolights (Flashpoint 620m), and use the flash activated slave. My Nikon d50 doesn't support PC Sync. Will this work? Are these reliable monolights?

I'm glad I opened your question. I have used the Flashpoint monolights for years. I have two of the 620s and two 1800s. The 620 light is ideal for typical studio work. My 1800s are actually too powerful for anything other than large groups in large arena type areas. I have never had any problems with any of the lights, and have never even had to change the modeling or strobe bulbs. They have a consistent color temperature of 5600K at all power levels. Just set your camera kelvin temp to 5600 and you will never have to worry about white balance. The power level adjustment knob lets you adjust power to any level, though a digital readout of power level would be nice, but not required.

As for them working with your SU 800, I can't speak to that. I have fired mine from day one with the infrared trigger that is made for those lights. (It is sold through Adorama, you sometimes have to hunt for it).It is a trigger that mounts in the hot shoe of your camera and will fire the Flashpoint lights. My guess would be your SB 600 could be used to trigger the Flashpoints. I have had them fire when I was in a large event when the flash of other people's cameras were going off near the Flashpoint lights. But the infrared trigger is cheap and I think a much better solution for firing the lights.