I ordered some of those SmArt stencils from nail delights, and they do work on Shellac, though I have to say I'm not overly impressed with the stencils in general. I find that they are most effective if used with additives, particularly if you do a colour fade over them.
I've tried doing the full nail in Shellac then using more shellac over the stencil before removing and curing and I didnt like the result at all, very amateur looking, same with glitters, not impressed at all.
To be honest with the exception of a very few I think there are better ways to do your nail art than with the stencils, they very much remind me of a DIY product and I would happily retail them but I'm not going to use them on clients, with the exception of the skull & crossbones one which I use with additives and it looks great :biggrin: