Ok DBU has a reactive reducer that is used in it , it actuallly is a catylised base.( after reduction it has a pot life (will turn to jello like substance after a few hours and cannot be reused.)

DBC uses the same reducer as their clears there- fore a tad cheaper as you dont need to buy 2 seperate reducers .1 for base & 1 for clear.(DBC when reduced can be reused IF the DBC hardner isnt used. )
But DBC has a catylist the can be used in it to make it dry faster . Then it just makes it about the same cost as using DBU.
Both are excellent products just depends on what you want to spray, they spray about the same .