I just saw this video the other day and it is a really great idea for applying a holo topcoat to other nail polishes. It's the water marble technique, but instead of making a bulls eye of different colors, you are creating one layer of the same holo polish. I used the silver Sally Hansen Nail Prism holo. It's not a very strong holo, but it's the only silver holo I have.
In the last two pictures, the red nail looks a bit wonky from the water I have to use (bottled water in Germany doesn't respond well to water marbling like it does in the US). But in general, the nails look more even (at least to me).