The Quad is an external box, it changes nothing in the ECU. The Smarty changes the ECU programming and leaves no trace of that having been done.

Either one will leave traces of more than normal operation in the snapshot data streams if a DTC is present. Can't change it, can't stop it, can't erase. The only good thing is it takes an experienced tech to be able retrieve and interpret the data.

Those are relatively few. Unfortunately, the OP's dealership seems to have access to one that knows his way around.