I know that this product isn't eveyone's favorite, but if you master how to use it, it works great.
First, you have to push down fairly hard on the center spring to make sure that your paper or the cutter doesn't move.
Second, MAKE SURE that you are using the center circle to turn the cutter, NOT the ruler arm/blade! This is the biggest mistake that I have seen people make. This is what is going to cause an uneven cut.
I really like this product and I like the range of circle sizes that you can cut with just a loosening of a wheel. :)