Keywords are supplied with accurate, clickstream-based metrics, some of which are exclusive to Ahrefs. For example, Clicks and Clicks Per Search can give you a better idea of how much traffic your content can get. That’s a burning issue today – many queries never translate into clicks because Google reveals answers for them at the top of SERP (i.e., Knowledge Card).
* Please note our tool currently assumes Google having ~ 83% of the market, with Bing + Yahoo! splitting the remaining 17% of the market. Actual market conditions may vary significantly from that due to a variety of factors including: search location, search market demographics, how much marketshare mobile search has relative to desktop in that particular vertical, etc.
In a nutshell, Long Tail Pro helps you quickly find keywords in bulk based on a seed keyword that you input.  In addition to returning hundreds of related keywords, the tool also shows search volume (monthly search volume), advertiser bid, number of words, rank value, and my favorite Keyword Competitiveness (helps you judge the competition and keyword difficulty).