Strobist is running a two part series comparing the Ray Flash v. Orbis v. AB 800 Ring Flash
You can find that series here.
I think there are a couple of important points to draw out:
1) Quality of Light is subjective;
2) The Ray Flash and Orbis are used on a speedlight, but can be mixed with studio strobes on or off camera. I’ve tested the Ray flash with my Canon 580EX II with excellent results;
3) They are great for both fill and key light applications.
These images were test shots mixing my Ray Flash and 580EX II on-camera with AB 400/800 strobes. I’m very pleased with results and the Ray Flash is a lot of bang for the buck.