One thing to keep in mind, especially for the L Bottom grapples, is that Loader lift ratings are typically measured at the pivot pins - the farther away you get from the pins the less lift capacity you get.
Loader type: Kubota LA525
Height (to pin): 94.3 inches [239 cm]
Lift to full height (at pin): 1131 lbs [513 kg]
Lift to 1.5m (at pin): 1490 lbs [675 kg]
Lift to 1.5m (at 500mm): 1182 lbs [536 kg]
That last one is the important one - after factoring in the added length of the SSQA, 500mm (or 19.6") forward of the pins would put the lift point roughly at the rear third of the loader bucket, where presumably your main load would be.
So for roughly 20" from the pins you get 1182 lbs of lift - 450lbs grapple = 732 lbs net lift. The further you get out on the tips of the grapple tines, the lower that net lift becomes.
Now there are "tricks" like curling or dumping the grapple so that the load is now further back & closer to the pins but since you haven't purchased a grapple yet, now is the time to maximize your net lifting ability.
I understand about the "single source" benefits from getting everything thru your dealer, but why not talk to him and see if he's willing to have you buy the EA grapple & ship it to him for mounting / testing prior to delivery to you?
I know EA actually has a couple dealers that are ordering grapples from them now so it might be a win for the dealer as well.
Cost nothing to ask, worst he can do is say no.
Best of luck whatever you decide to go with.