Thanks for getting in touch! For the annual PLUS plan, we do charge the entirety of the fee ($47.88) up front. After paying that, you will not be charged again to gain unlimited access to workbooks and advanced features to create custom workbooks.
If you purchase the monthly option, you will be billed $4.99 per month, and will get access to two ready-made workbooks per month, plus advanced features.
I hope that helps! Please contact our support team at firstname.lastname@example.org if you have any additional questions.