I, too, am interested in the pros and cons of a 4n1 bucket. I think of two cons right away: very expensive, hence depleting your wallet, and heavy, hence depleting your hydraulic lift capacity.
What are the 4 functions? As I understand it: regular bucket, grabber, bulldozer, backgrader. I can see the grabber as being useful periodically, as a more efficient alternative to loading logs, rock or brush onto forks. Then I ask myself whether there any significant benefits to the bulldozing and backgrading capabilities versus a regular bucket, which can sort of do both, plus other implements I may have.
So far, I can't convince myself that, for my applications, the device is worth the cost or the loss in lift capacity.