I think it's worth pointing out there's two types of ring flash:
Ones for macro use are intended for close up work where a normal flash would be obscured by the lens. They're normally low power as they don't need to throw light a long way.
Ring flashes for portrait use are much higher power, intended to light a much bigger area. Both intend to give even, shadowless light, but portrait ring flashes use a bigger light source to try and soften the light. Recently a couple of clip-on solutions for standard flashes have become available. The established one at the moment is the
Ray Flash ringflash adaptor.
Try and mix and match and you'd struggle to get good results.