Here's my take on this subject.
I installed 3 rear remotes shortly after purchasing our TC-40D so certainly there was an available rear remote that we might use for the grapple.
I didn't want to stretch hydraulic hoses from the front to the back of my tractor underneath where they were prone to added damage from snags with immovable objects.
When using the joystick to raise/lower or curl the bucket it's second nature to push a button on the joystick in order to gain control of the grapple without having to remove your hand from the joystick, without needing to move your hand and attention to the rear remote lever to open/close the grapple.
Your productivity will increase using the button on the joystick as all movements will be automatic and fluid. I have found that when working in the woods the grapple circuit became automatic to me in a very short time.
When you factor into consideration the increased cost of the longer hydraulic hoses and the rear remote kit itself it'm not sure you are actually seeing any big bucks between the two installations.
The electric diverter valve that we purchased from
Surplus Center was $149.00 at the time of our installation, although they have gone up some since everyone here at TBN started adding the electric diverters to their own rigs.
In short controlling a grapple can still be done with a separate rear remote by stretching hydraulic hoses under your rig if that's the route that you choose to take.