They don't appear to be a full ring. I don't know what your intended use is. If purchasing be sure it will fit your lens. You might also consider a bracket from Bogen/Manfrotto that you can attach two conventional flash units many available or that you may already have. The bracket can be adjusted to have the flashes at 45 degrees or pretty much any angle. Each flash can be set at whatever power you want. You would need a PC cable that attaches both or a peanut slave for one. Shadowless light especially if glass or reflective subjects are involved and the flash unit(s) can be used without the bracket for other types of images.

http://www.jeffreyglasser.com/