Dealer is probably recommending the grapple just based on what he sells. While 620# isnt too hateful especially considering its a 72" and double lid. The tomahawk, which is the same brand as mine, is 535# for their 72" dual lid grapple made from 1/2" steel as well. Mine being single lid, 66" and 3/8" plate is a 415# grapple.
Hard to tell on price if its a good deal because whats the breakdown? How much is just the grapple? and how much for the 3rd function?
Why did you not consider a diverter? I installed my diverter in just a few hours and had $225 not counting the couplers. Need two sets to attach the grapple, and they can range in price from $5/pair up to $60+ per pair just depends on what you want to go with. I had originally went with 1/2" flush face like most skid loaders. Didnt like them but dealt with it.
When it came time to install my snowplow, I swapped them to standard 1/4" parker 60-series couplers. Which is what ALOT of old meyer snow plows have, and I have a ton of them.
So....you could potentially have a diverter for ~$250 done yourself......and a ~$1100 grapple for a total of $1350 and a few hours vs $3200+ at the dealer. I am sure the blue diamond cost more. But it all comes down to how much you value your time. I dont value my time as high as the dealer, which is why I do most stuff myself.