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).
Long Tail Pro is a keyword research tool that helps you quickly find low competition keywords for your website. In particular, the tool is built for people doing SEO (search engine optimization) as opposed to people doing paid ads (Google Adwords PPC). I'm sure there are some advertisers that use the tool for paid ad keyword research, but the tool was built for SEO keyword research.