The 60" Millonzi has two jaws and weighs quite a bit more (I think more than 125lbs) than the 48" version. I did not realize the WRLong 60" was only a few pounds more than the WRLong 48". The WR Long 48" is about 50lbs heavier than the Millonzi 48 however. I do like the wider jaws on the Long...although the biggest problem I have with my
grapple is related more to small stuff (less than 12 inches long) falling through the
grapple rather than big stuff falling out the sides. Still the wider top jaw looks like an advantage at a cost of a little extra weight. Looking more closely at the two brands I'd say at the 60" length the WR Long looks better due to the weight advantage over the Millonzi. The two jaws on the Millonzi 60" version might be important for demolition debris but I doubt it is important for brush. At the 48" length I'm not sure the wider jaws are worth the 50 lbs.
For me the cost of the Millonzi 48 was less than half of the cost of the WR Long equivalent when I priced them. To be clear I got the Millonzi direct from the factory off Ebay and I don't know if they do that any longer as they try to build up dealer networks. My quote on the WR Long came via Carver (or was it Carter?) in NC if I recall correctly. The cost of the QA adapter needs to be considered as well and I gather this is included in your quotes.
I'd check the price on the 48" Millonzi set up as I do think you'd be happy with it. If the price difference is negligible then I'd be inclined to go for the WR Long 60.
$1750 may seem like a lot for an implement but grapples are so useful for brush clearing that I'd do it again in a flash at that price.
Two more photos: First is biggest load I could get with bucket and toothbar alone without getting off the tractor to secure the load

vs. second photo with biggest load of brush I ever got with one bite with the
grapple
. Or, I could have titled the photos: this is your tractor and this is your tractor on steroids.
