Think of the machine as the lifting power, the plate as the fulcrum and the grapple as the load. 20kg at the plate requires less lifting power to hoist than 20kg out on the dangle grapple. You can say that's either wood or rotator out there on the grapple and what's 20kg either way but IMO you'll quickly wish it was 20kg of wood or more capacity.
Running machines efficiently is all about pushing them to their capacity, and ime with a grapple you'll quickly find that point and wish their was more. What capacities are you playing with on that lifter of yours?
Don't discount the loss that a dangle grapple will have. My little ramrod could do about 800pds in a bucket, about 500 with the bmg 50pds less would've been sucky for me. But I imagine you have much higher capacity?
Lastly I'd consider the robustness of the rotator and the extra hoses and switch for changing between rotate/clamp. I know I beat the living hell out of my grapple but maybe I'd have been a little less aggressive if things were exposed like on that avant.
Hopefully Carlito will pipe in, and others with their experiences.
I doubt you'd hate either one.