I did this at someone's request but I thought I'd post it. I don't have Charla, so I used Orly Halley's Comet instead.
L to R: Kotori, Crystal, Halley's Comet
At this point Halley's Comet was opaque so I didn't add any more.
Four coats (three coats of Halley's Comet):
At this point Crystal was opaque, so I didn't add any more.
Five coats of Kotori, four coats of Crystal, three coats of Halley's Comet:
With top coat:
As you can see, they are very different. Kotori, the sheerest, is a dark charcoal base with lots of blue microglitter. Crystal is a metallic light blue with lots of gold flecks. Halley's Comet is teal with yellow-green sparkle. From what I have read, Charla is slightly more blue and more sparkly, but they are very close. All of these formulas were very easy to work with and dried fairly quickly.
In conclusion, these three colors really aren't similar at all and it's worth having all three!