We have been using this software for several years and it has worked perfectly for us.
We sell everything from individual downloads, to large home study courses with more than 2 dozen files, downloaded from a secure private members only site.
Sam even showed us how to sell a package of several home study courses, each with its own download website, all with a single username/password for the customer.
We even sell our physical products via DLG, so we can include free bonus downloads.
Best customer service on the internet, and a fabulous forum with great ideas from Sam and his DLG users.
If you sell on the internet, check out DownLoad Guard. You will be glad that you did.