It is my understanding that the Canon life size converter actually converts the 50 macro into something like a 70 macro, so it might improve working distance slightly compared to the 50 and an extension tube. If you've already got the EF 25, why not try it and see what you think? There are many happy folks getting macro scale images with extension tubes, closeup lenses and the like. I don't know if the EF25 gives you enough extra focus to get to 1:1, but you can find out by looking at most EF lens brochures, or calling Canon at 1-800-OKCANON.