Well, which Jazz bass did you compare them to? There are so many J pickups out there, it's hard to generalize. It's also hard to say if YOU would prefer the sound of Fodera Duncan Js to their duals split
But chances are that their J pickup will sound more like other J pickups, so perhaps less to your liking?
My guess would be that to get that sound in a J pickup, you might want an underwound J pickup. That's really a guess, based on some vague recollection about reading on Fodera Duncan duals... Or simply talk to folks at SD whether they can wind you a pair of J's based on their Fodera Duncan duals split. I'm not sure if they can do that, but worth talking to them...