This tool has many functionalities (and more that are releasing).
The most important for me are:
1) Information on competition keywords and organic traffic.
We can see the traffic of our competition and the keywords that have positioned and what % of traffic takes each one.
It estimates the visits that any website you want to know more information about. It tells you exactly which keywords are the most traffic generated for the web you want, in any language or version of google.
2) Search related keywords
It gives us information about similar words or synonyms.
3) Domain analysis vs. domain
We can make comparisons between different domains.
4) Ranking of the keywords
You can get reports of what words the domains have positioned. Which has won or lost since the last time. Ideal to monitor the evolution and track a website and our competition.
In my opinion, the biggest weak point is the estimate of visits made by the tool, which is not reliable at all. I have checked with domains that are making an important advertising investment, and the tool fails a lot in its estimation, giving values much lower than real.