Hi James, definately finer grain and better film speed. Undiluted it's a fine grain developer like D76/ID11, with all the pros and cons, good for pushing to the limits. 1+2 is sharper with more visible grain but still a lot finer than with Rodinal. Especially visible with fast films of course.
Biggest advantage of Caffenol is imo that - no matter how much or how few films you develop - you always have a fresh mixed developer and don't have to spend a single thought on shelf life and environmental effects.
I surely forgot a lot to say, but have to go to work now.