actually it pretty popular ,
they are locked via social accounts, and once you are registered via facebook, you constanly receive emails about new answers.
check their semrush rank
[TABLE="class: sem-report-block-summary-table, width: 218"]
[TR]
[TD]SEMrush rank[/TD]
[TD="class: right, align: right"]597[/TD]
[TD="class: right, align: right"][/TD]
[/TR]
[TR]
[TD]Keywords[/TD]
[TD="class: right, align: right"]536K[/TD]
[TD="class: right, align: right"]+11%
[/TD]
[/TR]
[/TABLE]
there are ranked on top 20 for over 530k keywords and thats only from semrush data
so there is huge traffic source.