Merging, e.g. from a ramp to a highway, is a potentially complex operation that frequently requires cooperation between the involved vehicles. Besides safety aspects, it can also lead to significant traffic flow disturbances. While V2X and automated driving might reduce or even solve the problem in the future, mixed traffic, including human-driven vehicles without V2X, will be the norm for a while. This paper proposes a cautious merging assistant based on MPC, which does not only ensures safety but also minimizes the induced disturbance of the traffic flow. As an indicator of the induced traffic flow disturbance, we propose a function related to only readily available measurements of the first disturbed vehicle. The evaluation is done using a catalogue of merging situations extracted from the "HighD"dataset and confirms that the cautious control does indeed provide a safe merging while affecting less the incoming traffic.