Is it manual or ETTL? Even with the third-party ETTL implementations (Sigma, primarily), it can't beat Canon's for reliability and accuracy. And if it's manual, you can still live with it, you'll just have to bracket more and be thinking about your power settings. Basically, you'll probably lose plenty of shots that you'd have gotten if it was an MR-14/24.
While I don't completed agree with the above, do you currently have a flash? I get good results from a hotshoe flash and off camera cord, much cheaper (since I already had the flash) then another flash.
If you post over on the Macro forum, you'll get plenty of advice on how to use a plain strobe off camera to get great macro lighting. Dedicated macro ring lights can be useful but seem to have lost favor amongst the serious macro shooters.
Ring lights for 35mm cameras were originally created for medical documentation where the goal was shadowless illumination. The flat lighting they produce isn't particularly well suited for applications where normal 3D modeling is required. I don't shoot bugs very often, but when I do I light them the same as any larger subject with a pair of flashes. These were all done with a pair of Vivitar 285HVs. By no means the epitome of macro, but they illustrate what can be done with a couple of very cheap flashes, one on a flash bracket and another off camera
