It replaces the function of the points, condenser, and mechanical advance mechanism (we all know how twitchy the advance gizmo is) and provides electronic switching to the coil and a choice between several selectable timing advance curves. Plus, you leave your old stuff in place thereby giving you a redundant ignition triggering system.
Probably all of your questions can be answered here:
http://www.stephenbottcher.net/~omega/omega11.htmIf this doesn't do it then shoot Stephen an e-mail. He's a very nice guy, I've met him at a couple of rallys as he usually trys to cycle down to OK to catch at least one of Ken's rallys per year...