What does the software or service do well? It scans (crawls) websites for areas of opportunity to improve SEO. It trends the data so you can see the growth per your actions. And it provides excellent hints to help you along if you aren't an SEO expert.
What does the software or service not do well? For what it is designed to do, I can't think of a negative.
What do you wish you had known about the software or service before using? I wasn't aware how much of a platform it really was. It's very big, and has a little bit of a learning curve, but not nearly as difficult as some of the other tools it competes with. So, it was actually a good surprise!
Have you used a competitor to the software or service? If so, how does it compare? I have. Sitebulb has become my top choice.