It may be different with your college (I'd double check with them) but usually a Diploma is worth 2 A levels, and an extended Diploma is worth 3.
As for if it's easy.. I sadly can't answer that as I've never looked at it. You could look at the specification though to see the sort of content you'd be covering. Although it will contain all the units and you may not do some of them, it gives a general overview of the level you'd be working at and the assignments you'd be completing