Andrew Left is bullish on shares of Twitter at its current price level.

Despite being much maligned, Twitter is "a compelling product," Left said in an interview Friday on CNBC's "Halftime Report." "When you compare the market cap to Facebook, it has a long way to go. … It's a compelling platform for where its trading."

Twitter had a market value of nearly $18 billion as of midday Friday versus Facebook's $547 billion market cap.

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Left, who is known for his short-selling bets against companies, said his firm is long Twitter shares. He said Twitter's competitive position in the social media space is underrated.

"You can see the engagement levels on Twitter and the relevancy it's playing in our society can't be denied," he said. "They dominate that space of social media."

Greenlight Capital's David Einhorn also revealed in a note to investors that his fund bought Twitter shares on Jan. 16.

"Despite a massive user base and broad reach, Twitter has an enterprise value of about 2% of Facebook, the largest social media platform," Einhorn wrote.

Left gained notoriety for successful bets against stocks such as Valeant Pharmaceuticals. He is known for his bearish company-specific reports published his website Citron Research.

Shares of Twitter were up about 8 percent Friday.