Is the Valsalva Maneuver safe?
Yes, it's safe. It's taught to scuba divers as a standard method for equalizing air pressure, with the general caveat that it should never take too much effort and if you feel any pain or discomfort from doing it then you should stop diving and consult a doctor. Since pressure changes in the air are much more gradual than those underwater, it shouldn't be difficult at all to equalize in an aircraft.