Hi Ken. One of the most important differences between DF and DR is that DR has the create user account function (which is not present in DF). DR also has the ability to update user profile whereas DF can only pull from the profile to auto-populate fields but not to update profile.
Having said that, DR and DF have pretty much the same capabilities especially when it comes to PayPal, role assignments, email events, etc.
Based on what you said above, you probably would be better off with Dynamic Registration. Another option is to let your users register with standard DNN registration then control their access by roles which can be assigned by DF after payment. Many of our users actually use both modules on their sites.
Candace