Like what some of the members said,
if the Pay Site's video that you're promoting is difficult to find on torrents and other free tubesites,
it's a good go,
but I would say that most adult sites work best with pop-ups and pop-unders especially mobile redirect,
you get around 2.1 per cpm that's USD$2~2.1 per 1000 views,
imagine your site has around 100k views per day, that's $USD100 / day easy with pop-unders,
as most porn tubers are freebie seekers it's difficult to convert,
but I'm not saying you shouldn't try,
if you want some good popunder sites you can pm me and I can list a few that i've tried and filtered to this day,
Thanks