My $.02 is that a 3rd function is not an ideal solution for a grapple. The problem, at least for me, is the third function has no practical way to moderate the speed and force of the hydraulics that open and close the grapple. I had one installed on the last tractor I bought , used it for a day or two, added a flow limit valve which did not work, and went back to using the rear remote to operate the grapple so I could control it through the use of a real valve.
For the same money I could have added at least one, and maybe two, more remotes.
Yes you take your hand off of the loader valve. So what? On my tractor they are located adjacent to each other and it has no real effect for me.
As I said just my $.02.