It does give you about 3" (9 cm) extra working distance compared to the Canon 100mm lenses, but that advantage comes at a cost. It is half again as expensive as the 100L, and more yet compared to the 100 non-L. It weighs a full pound (about 400 g) more than the 100L and is longer, meaning it is much harder to manage hand-held. If you want to go to higher levels of magnification, the impact of extension tubes gets smaller as focal length increases.
that said, although I shoot a great deal of macro, I have no personal experience, since these factors have been enough to persuade me not to buy one. On a crop sensor camera, I use a 60mm macro for a lot of flower shots and a 100mm L, often with a 36mm extension tube, for bugs. Yes, you have to get very close for 1:1, but with practice, it is doable.
I have no experience with Sigma or Tamron macro lenses.
100mm Canon macro, 36mm extension tube, 50D: