The router manufacture are doing their very best to confuse you. They quote the rates adding the rates together but this is being intentionally deceptive. The router can run both radios simultaneously but they neglect to point out that it must run to different devices. The end device generally only have one radio chip so can only run 1 band at a time but even if they had 2 radios both the router and end device would need special drivers to bond 2 radio signals into session. It is technically possible I suppose but I have never seen it done. There is some specialized outdoor point to point equipment that does it.