What I understand is a 3rd function is different than using a diverter valve setup, with a diverter setup you have turn, push, pull, hit, yank, move a switch so the curl function for the bucket operates the grapple thumb, and that's how the feathers start feathering. I feather my bucket all the time when curling.I have the 3rd function and have not noticed an inability to feather the grapple function. I have heard this before but don't understand it. I don't know if my grapple has flow restrictors or if my pump is so slow as to not cause problems. But I can pick up a sheet of tin and not dent it but the hold the button down and put the grapple teeth right through it.
Where did you get your 3rd function button setup, I'm leaning in that direction until my wallet says other wise.