Traffic stop

One of the types of popular websites does what we've doing in this exercise: measures the amount of traffic websites get. If this seems somewhat circular then that impression will not be alleviated by repeat mentions of Alexa and SimilarWeb.
You can do an Alexa ranking of itself

The amount of traffic a website gets has become of utmost importance to Internet marketers and SEO is a big part of their strategy. Search engine optimisation sends your website on weight loss programs or eCommerce to the top of the search rankings so it gets seen before those of your competitors and gives you more chance of sales. This is not to say that the sites with the most traffic are commercial or have been engineered to attract said traffic; there is a case for 'build it and they will come' which is why Google, Facebook and Yahoo! are so popular. But as search engines, social media and email platforms of the past have shown us, this cannot be guaranteed indefinitely (though I do suspect that Duck Duck Go's attempt to steal Google's thunder will only gain so much traction)

But, yes, buying those ads to appear above the natural ranking when one searches for 'sites that measure website traffic' yield
[about 3,820,000 results]

Ads

1. Measure web traffic | And get more profit | SEMrush.com‎

   Adwww.semrush.com/Website_Stats/Traffic_Tool‎
   
   Try out our ultimate SEO tool and increase your web trafic. Register now!
   Pages/Visits · Find site traffic sources · Traffic Rank/Bounce Rate · Average visit duration
   Services: Keyword Analytics, Site Audit, Traffic Analytics, Position Tracking, Organic Research, Backlinks

   • Site Audit

     Free Online Website Checker
     Over 100 on-page & technical checks

   • Organic research

     See Competitors’ Best Keywords.
     Observe position changes of domains

2. Website Traffic Analysis | Use Data to Build Better Sites | mixpanel.com‎

   Adwww.mixpanel.com/web-traffic/analytics‎
   
   Understand User Behavior & Make Stickier Products. Sign Up for Free Today.
   Services: Engagement Measurement, Retention Tracking, Funnel Visualization, A/B Testing, Notifications

3. Drive + Traffic To Your Site | Get Discovered on Top Websites‎

   Adgo.taboola.com/Traffic‎
   
   Taboola Reaches Over 1 Billion People Every Month. Start a Campaign for Just $10
   Drive Growth · Increase Traffic · Optimize Conversions · Promote Content

4. Free Web Traffic Quote | Submit Your Site - Free Quote‎

   Adwww.wmegroup.com.au/SubmitFreeQuote‎
   

   1300 663 995
   We'll Get You Page 1 Rankings! Submit Your Site for a Free Custom SEO Quote.

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So, have you heard of Semrush, Mixpanel, Adgo.taboola or WME group? Nope, me neither.

The same can be said for the organic top rankers: Incomediary, Labnol.org, Moz, socialmedia.biz, Ahrefs, and Digital Deepak or the further ads at the bottom of page one for Kissmetrics and Pop monetize. The two top ones Alexa and SimilarWeb are familiar - now. Makeuseof also makes a reappearance.
There is no reason, of course, that sites that measure website traffic will themselves attract it.