For $400 you get the whole bike. The Bontrager crank costs $159. Is there a good reason why you'd want to spend 40% of the cost of the bike on a different crank? It's not like it's going to be any better, in my opinion.

From you not knowing that the Bontrager crank was a integrated crank, I'm led to believe you're not really sure what you're buying. Do you know what you're getting?