I've used it with some good results, although I must say the results have varied greatly... I was able to get over 80 backlinks with one article, but others haven't done as well. There are a lot of variables to consider. It's possible that it does better in some niches than others. It takes experimentation to find out what works best...
I used it for three months, and really enjoyed the results. You can get good ranks on longtail keywords very quickly. If you're willing to put in some extra effort and put in a spinnable version of the same article, it will get picked up a lot more.