SUMO was never finished and released as by the time development proceeded there were already several great components out there that did what SUMO was going to do - but they did it much better.

SUMO was meant for Subscription Mambo, meaning you could allow people to use PayPal subscriptions in order to allow subscriptions for access to Mambo.

The product I now recommend for doing this is called http://www.joomlapal.com/