Looking at the pricing page
The Pro License says it is Perpetual (one payment) but then says Per Year next to the price. Is it once off to get the product and yearly to get updates (optional). Is this correct?
I think your understanding is correct. From the Pricing page, further down in the “frequently asked questions” section:
Is this a subscription or a perpetual license?
Perpetual, with a yearly maintenance renewal. You are allowed to use any release of Hangfire Pro that was available when you purchased the subscription, as well as any future releases (including new features, bug fixes, etc.) for 1 year from the date of purchase.
After that 1 year, you can continue to use the version you have forever, or you can choose to renew your subscription for another 12 months to continue getting updates. By renewing annually, you help me to continue to innovate and add new features to the product.