WPSmartpay has knocked it out of the park in terms of simplifying subscription forms and digital product sales. The donation format is a plus for agencies that have clients in need of that feature. Cost? Compared to some of the annual fees charges for WP plugins that offer similar aspects to utilize, the appsumo deal is well worth consideration. I am using said plugin on several sample sites to determine how best to incorporate it on other platforms and I have found it to be easy to use and would suggest looking at the Smartpay youtube video that explains the beginnings and tips to use for amplifying what one can do with it from start to finish.