It's pretty insane to me that someone would trust their life 20 meters above the water to a rope swing put in by some rando. What if the rope snaps or becomes detached from its anchor? What if the rope is way too long and you dislocate your shoulders hanging onto it on the way down? Or if you let go midway down because you realize it's too long, if you belly flop into the water, pass out, and drown? What if the rope wraps around one of your limbs?

I wouldn't trust this thing 3 meters off the ground. This is just begging for a hospital visit, and that's if you're not too unlucky.

(This isn't really close to terminal velocity, by the way.)

12-25 seconds is what it takes to reach terminal velocity. 1500 feet/450 meters is a conservative data point.

80-ish feet from this isn't approaching terminal velocity.

The only way I could think to make it work would be to run along the cliff edge to the swinger's left and then jump in order to get the rope taught. Only issue there is you better be damn sure you leg go at the right time or it will be sending you back toward the (presumably) shallow rocky water at the cliff base.