Generally speaking they are brilliant.
Chord detection works best on single instrument tracks. Think piano or cleanish guitar. Does a decent job on distorted guitar tracks. But the killer feature is after a chord track is setup and all tracks (obviously not percussion type tracks) are enabled/linked you can change a chord on the Chord Track and it automagically changes all the supporting tracks. It's pretty sick if you don't try to over use it (by moving the chord beyond it's ability).
Arranger track is killer too.