Films on Demand tends to be documentary/educational media (as opposed to dramatic/fiction works). Films are broken into segments, making it easier for you to share a very targeted topic with your class -- but you can also link or embed the entire film.
FOD uses a patron-driven acquisition (PDA) model, but we can also purchase films directly for a one year license. While the PDA is funded, all FOD films are available to watch. After that money runs out, only the licensed films (those purchased directly or those that triggered a purchase because enough people watched them) are available until the budget year starts over.