You can do either/or with age oath.
If you link straight to yourdomain.com/url you get recurring.
You can use the linking code they give you and make $40 per sign up that way, same as if you were promoting someone else's Age Oath site. ($30 for the referring webmaster, $10 for the site owner, so $40 if you refer to your own site)
Point is, you don't have to decide now before you build or submit the site. Try both and see what works best for you.
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Did somebody say Free Content?