Hi Maximilian,
As Markus states the Simple Commerce Module is as its name implies fairly simple. At the moment it only works with PayPal and I am guessing that this will probably stay this way. Having said that though PayPal is exceptionally widely accepted as a payment method nowadays and on the whole makes for a trusted environment for users.
You do have to have users logged-in for the module to be able to log their payment so if you are offering downloads you would have to ensure this happens or else there would be no way of them coming back to the site after payment has been made so that they can download items. If the system doesn’t have a record of their payment then it would be impossible to say what that person can and can’t download.
Having said that the work-flow process of all of this can be handled very easily and I have done this on two sites now. All I do is have conditionals that will not allow the payment buttons to display if a person is not logged-in / registered but instead I show a message to say something along the lines of :
“You need to register or log-in to be able to purchase items from us.”
As I have told them this and provided the links to log-in or register right there for them then the process isn’t that long winded for a person. Doing it this way also prevents them from adding anything to a PayPal shopping cart because until they are logged-in EE will not be able to track the sales.
Once they are logged-in then the PayPal buttons will appear and they can start to add items to the cart.
After they have added as many items as they wish to their cart then they pay in the normal way through PayPal and they can then come back to the site to a :
http://www.mysite.com/downloads
area and see the items that they have purchased. This can be handled very simply with a plugin that basically queries the EE database to see if that logged-in member_id has a payment in the Simple Commerce Module table for the entry_id they are viewing. You can then output links to the items for the person to download.
I handle this part using a script from Vibralogix.com called LinkLok URL. I had to get a couple of very small changes made by the author of the script so that it would work being included as a PHP file inside an EE template but once I had that then I had a complete downloads process up and working.
All is definitely doable but depends on how much time you want to spend on getting it all to work the way you want it to.
Hope that helps.
Best wishes,
Mark