Unless you have an insider at the banks for something like 'staff rates' or you are changing some significantly large figures, or you don't want to risk walking around with cash, banks are thieves. There are bureaus with very good rates along Wabera street, the stretch starting from k-rep bank Kenyatta Avenue down towards City Hall way.
My take Westlands bureaus are a con & have bank rates or worse.
You kill bird...bird dead snake come.