Bob's Red Mill Low-Carb Baking Mix, so I made one of the recipes off the back to give it a try. It wasn't free, so this isn't a plug or a review.
I couldn't bear to have "just muffins," without a flavor other than "muffin." So I added cinnamon to the dry ingredients and made a low-carb streusel with brown sugar Splenda and cinnamon for the tops. These were decent as low-carb baked goods go, I just wish I had a better sense of what else I can do with the mix. I'm not sure exactly what it can substitute for. The texture of these muffins weren't any better/worse than some of the paleo banana bread I have made in the last year. Which means you can use the mix instead of starting from scratch, but I'm not sure it is as cost effective.