Is $8,400 to replace roof with GAF Timberline HDZ shingles (gun nailed) a fair price?

I need to replace my roof and got two very similar quotes with one big cost difference. I'm not sure what to make of the difference between hand nailing and gun nailing from a customer standpoint. Is there any performance difference? For example, is gun nailing more prone to errors that lead to leaks and lifting shingles? It seems crazy to spend an extra $1,800 if I wouldn't notice a difference, but if it does make a difference, I'd prefer to spend the $1,800 now rather than having to do a patch job or something like that down the line.