I've never gotten them but i know about them and will be taking a course that covers applying them. They last 2-3 weeks and likely won't effect your natural lashes, especially if you dont wear mascara with it since with removing the mascara it may also effect the glue (you shouldn't need mascara with them).
I have had them once. They looked great and didn't affect my natural lashes, but they were annoying (had to be super careful and use special face washes etc so the adhesive wouldn't dissolve etc) and they fall out pretty quickly. I think that if they were less expensive I'd get them but they just aren't worth the cost of getting them redone every few weeks.