You already own the domain (ie it was for an old side project you never proceeded with), the 7.99 would be to host the landing page, facilitate the payment, and help getting eyeballs on your list of domains.

Ok, I misunderstood the fee. I assumed that it was to have the ability to purchase domains. That makes more sense, and that model I like a lot more. I don't think I'd pay $7.99/mo for it though. At that rate I'd have to be kicking off a handful of dead domains a month to not lose money (time spent plus the fee), and therefore would rather just leave them be.

It wouldn't be per site fwiw, you could list an unlimited amount of domains for 7.99$/mo; consensus seems to be that a percentage is the better way to go though.