Ive done this twice this year, With amaising results, as far as hatch rates.
The thing is timing, if the males are not chasing the females hard, they are not ready, i tried a few with no luck but the ones that were "ready" the eggs just fell out of. with very little effort.
I think they drug the koi in the video to slow them down,(say no to drugs), but what I did with mine took 30 seconds or less, & they were back in the pond with less damage than the males would have done.
Same with the males as long as they were "in hot persuit" they were ready to go, & the milt run out of them with very little preasure.
I just mixed them together with a feather for maybe 5 min, in a dish, then added a little water & dumped on spawning mat in my tank.
I have thousands of babies that just hatched, just trying & keep a few hundred alive to see how they turn out is the hard part for me! lol
The first time I tried I lost 90% due to pure water quality, this time im putting them outside in green water, & let mother nature take care of them.