The standard diverter setup diverts a function from the noral 4 of the loader. (up bucket, down bucket, curl, dump) Usually the curl/dump functions are replaced with the grapple open/grapple closed function. This diversion only occurs when you press a little button. The default position is curl/dump. The only weakness of this setup is that you can't simultaneously curl and close the grapple. Folks with this diverter setup don't seem to have a problem with that. Too bad it's 400$, but that get's you a quality setup. Compare that price to adding a new rear remote and it seems in line with the costs of hydraulic stuff.
So far it seems that all of thse grapples utilize removable pins at the grapple hings and hydraulic mounts meaning you could remove those pins and take the grapple off for loader work if you felt it was in the way.
I would not recommend bolting any of these directly to the top of the bucket. Take advantage of this oppurtunity to build a stout platform for the grapple and a foundation for hooks.
It seems worth the extra 150$ to get the foundation frame that the green thumb setup lacks.