Its hard to say, but I can offer a general comment. Just faster. For me, I'm about efficiency, and I think 80% of my target recovery time is wasted with the pinpointer. My Carrot sometimes has no depth at all, and I have to test it against my digger. Half inch from the digger, no signal, so I have to power cycle it just to fix this. I sent it in to Garrett, and they claimed they fixed this, but they did not. I put it in the hole, no signal, put it near the digger, no signal, power cycle, wash rinse repeat. Very annoying, but it does work in the end.
It falses so much on the most powerful setting that it is useless in mineralized dirt. The mid setting seem to get a dime at no more than 0.5 to 0.75 inches. It needs more range, and needs more targeted range on dimes. I think what I don't like about it is that the field comes from the middle of the device rather than the tip, but devices claiming to be tip-active (and I forget which ones now) don't seem to work as well.
Its best feature is its ruggedness, but from what I understand, the orange material is less rugged than the old green material. Google "carrot condom" to see what others have done to fix this problem. Mine is not worn down yet, but it will be in a matter of time in our rocky soil. I just don't have the patience to deal with another after market fix for something like this, but it is much more rugged than the cheap knockoffs being discussed. That Harbor Freight one didn't last a month in the field for me.
So, "holy grail", that means pie in the sky wishlist: waterproof (Garrett is now), rugged (like the old Garrett green ones), orange (I like the Carrot because I was always losing the green one in the grass, but fixed that by tying pink surveyor's tape to it), tip-active targeting that works well, more range, and the real holy grail, discrimination. Show me if the target is iron like the old Sunray probes did before I get to it. I get the technical challenges to a motion discrimination pinpointer, but I know enough engineering to know that it is possible. It just may cost alot, but for me, it would be worth it to have this. You said "holy grail" after all