Well I'm still trying to get to the bottom of the best way of doing these crystal pedicures and I've got a set on my toes to test. I used a soak off gel, placed the crystals on the toes and cured. I then used Shellac top coat on one big toe and left the rest to see what happens. The crystals with the top coat have definitely lost some of their sparkle compared to the ones without but after two weeks all crystals are still in place on that top coated toe. The other toes sparkle like you've never seen but I've lost a few here and there. After saying that I did do this myself and was bending down for about an hour doing it, so I may not have done such a thorough job as if I was doing a client.
I think what I'm going to do is offer clients the choice, with or without top coat and if they choose not to top coat in favour of extra sparkle, then I will give them a few crystals to take with them to apply if they get any fall off!
Hope that helps a bit!