The counter alone does not require registration but when users click on it they used to show some stats you may not want others to see, however you can selectively disable those available to buyers and that stays in force even after the free or paid period runs out.
I tend to just sign up for a month at a time and as it requires a direct debit to be sent from PayPal, set it up join, then once the first payment has been made cancel the direct debit.
Don't bother emailing Sellathon to tell them to cancel it because you have to do that via your PayPal account.
For further details please look at the Sellathon site.
